| Message ID | xmqqilm51gn6.fsf@gitster.g (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2] diff --no-index: unleak paths[] elements | expand |
Am 03.09.22 um 01:49 schrieb Junio C Hamano: > "git diff --no-index" codepath starts with the two elements in > argv[] and munges them into two paths to be compared, stored in a > separate path[] arrays. The munging is implemented in a rather > haphazard way, sometimes overwriting old version with a new copy, > and sometimes a constant string assigned to path[], making it > impossible to release the resources properly: > > * A single dash "-" from the command line is a special signal that > the standard input is used for the side to be compared, and is > internally replaced with a copy of string "-" at a known address. > > * When run in a subdirectory, full paths to the two paths are > allocated and placed in path[]. > > * After the above happens, when comparing a file with a directory, > the directory side is replaced with the path to a file in the > directory with the same name as the file. > > This was perfectly fine for just two strings that are pathnames used > during the lifetime of the program and cleaned up upon program exit, > but it gets in the way when leak sanitizer is in effect. The third > step can be losing the full path that was allocated in the second > step, but it is not easy to tell if its input is an allocated piece > of memory to begin with. > > Loosen the earlier two steps a bit so that elements of the path[] > array that come to the directory/file comparison code are either the > singleton "-" or an allocated piece of memory. Use that knowledge > in the third step to release an allocated piece of memory when it > replaces the path to a directory with the path to a file in that > directory, and also at the end to release the two elements of the > path[] array as needed. > > Signed-off-by: Junio C Hamano <gitster@pobox.com> > --- > > * The previous one allowed strbuf_release() to free replacement.buf > which may be used in path[0] or path[1] potentially leading to > double freeing. The kosher way may be to use strbuf_detach() in > fixup_paths(), but this is a simpler fix, it is getting late in > the day, and I am getting sick of fighting the leak-checker, so... > > diff-no-index.c | 24 ++++++++++++++++++++++-- > 1 file changed, 22 insertions(+), 2 deletions(-) > > > diff --git a/diff-no-index.c b/diff-no-index.c > index 9a8b09346b..77a126469b 100644 > --- a/diff-no-index.c > +++ b/diff-no-index.c > @@ -208,6 +208,14 @@ static void append_basename(struct strbuf *path, const char *dir, const char *fi > strbuf_addstr(path, tail ? tail + 1 : file); > } > > +static void free_allocated_path(const char *path) > +{ > + if (!path || How can path be NULL? And if it was, why shield free(3) from it? > + (path == file_from_standard_input)) > + return; > + free((char *)path); > +} > + > /* > * DWIM "diff D F" into "diff D/F F" and "diff F D" into "diff F D/F" > * Note that we append the basename of F to D/, so "diff a/b/file D" > @@ -226,9 +234,11 @@ static void fixup_paths(const char **path, struct strbuf *replacement) > return; > if (isdir0) { > append_basename(replacement, path[0], path[1]); > + free_allocated_path(path[0]); > path[0] = replacement->buf; > } else { > append_basename(replacement, path[1], path[0]); > + free_allocated_path(path[1]); > path[1] = replacement->buf; > } > } > @@ -274,6 +284,8 @@ int diff_no_index(struct rev_info *revs, > p = file_from_standard_input; > else if (prefix) > p = prefix_filename(prefix, p); > + else > + p = xstrdup(p); prefix_filename(NULL, p) is basically the same as xstrdup(p), so those two conditional branches could be joined. > paths[i] = p; > } > > @@ -294,13 +306,21 @@ int diff_no_index(struct rev_info *revs, > setup_diff_pager(&revs->diffopt); > revs->diffopt.flags.exit_with_status = 1; > > - if (queue_diff(&revs->diffopt, paths[0], paths[1])) > + if (queue_diff(&revs->diffopt, paths[0], paths[1])) { > + free_allocated_path(paths[0]); > + free_allocated_path(paths[1]); > return 1; > + } > diff_set_mnemonic_prefix(&revs->diffopt, "1/", "2/"); > diffcore_std(&revs->diffopt); > diff_flush(&revs->diffopt); > > - strbuf_release(&replacement); > + /* > + * do not strbuf_release(&replacement), as it is in paths[] > + * when replacement was actually used. > + */ > + free_allocated_path(paths[0]); > + free_allocated_path(paths[1]); > > /* > * The return code for --no-index imitates diff(1): Perhaps avoid the need for that comment by moving that strbuf to where it's used and have it spend its full lifecycle there? Something like: --- diff-no-index.c | 50 ++++++++++++++++++++++--------------------------- 1 file changed, 22 insertions(+), 28 deletions(-) diff --git a/diff-no-index.c b/diff-no-index.c index 77a126469b..9f8b78f173 100644 --- a/diff-no-index.c +++ b/diff-no-index.c @@ -196,18 +196,6 @@ static int queue_diff(struct diff_options *o, } } -/* append basename of F to D */ -static void append_basename(struct strbuf *path, const char *dir, const char *file) -{ - const char *tail = strrchr(file, '/'); - - strbuf_addstr(path, dir); - while (path->len && path->buf[path->len - 1] == '/') - path->len--; - strbuf_addch(path, '/'); - strbuf_addstr(path, tail ? tail + 1 : file); -} - static void free_allocated_path(const char *path) { if (!path || @@ -216,12 +204,28 @@ static void free_allocated_path(const char *path) free((char *)path); } +/* append basename of F to D */ +static void append_basename(const char **dir, const char *file) +{ + const char *tail = strrchr(file, '/'); + struct strbuf path = STRBUF_INIT; + + strbuf_addstr(&path, *dir); + while (path.len && path.buf[path.len - 1] == '/') + path.len--; + strbuf_addch(&path, '/'); + strbuf_addstr(&path, tail ? tail + 1 : file); + + free_allocated_path(*dir); + *dir = strbuf_detach(&path, NULL); +} + /* * DWIM "diff D F" into "diff D/F F" and "diff F D" into "diff F D/F" * Note that we append the basename of F to D/, so "diff a/b/file D" * becomes "diff a/b/file D/file", not "diff a/b/file D/a/b/file". */ -static void fixup_paths(const char **path, struct strbuf *replacement) +static void fixup_paths(const char **path) { unsigned int isdir0, isdir1; @@ -232,15 +236,10 @@ static void fixup_paths(const char **path, struct strbuf *replacement) isdir1 = is_directory(path[1]); if (isdir0 == isdir1) return; - if (isdir0) { - append_basename(replacement, path[0], path[1]); - free_allocated_path(path[0]); - path[0] = replacement->buf; - } else { - append_basename(replacement, path[1], path[0]); - free_allocated_path(path[1]); - path[1] = replacement->buf; - } + if (isdir0) + append_basename(&path[0], path[1]); + else + append_basename(&path[1], path[0]); } static const char * const diff_no_index_usage[] = { @@ -254,7 +253,6 @@ int diff_no_index(struct rev_info *revs, { int i, no_index; const char *paths[2]; - struct strbuf replacement = STRBUF_INIT; const char *prefix = revs->prefix; struct option no_index_options[] = { OPT_BOOL_F(0, "no-index", &no_index, "", @@ -289,7 +287,7 @@ int diff_no_index(struct rev_info *revs, paths[i] = p; } - fixup_paths(paths, &replacement); + fixup_paths(paths); revs->diffopt.skip_stat_unmatch = 1; if (!revs->diffopt.output_format) @@ -315,10 +313,6 @@ int diff_no_index(struct rev_info *revs, diffcore_std(&revs->diffopt); diff_flush(&revs->diffopt); - /* - * do not strbuf_release(&replacement), as it is in paths[] - * when replacement was actually used. - */ free_allocated_path(paths[0]); free_allocated_path(paths[1]); -- 2.37.2
Hi Junio, On Fri, 2 Sep 2022, Junio C Hamano wrote: > "git diff --no-index" codepath starts with the two elements in > argv[] and munges them into two paths to be compared, stored in a > separate path[] arrays. The munging is implemented in a rather > haphazard way, sometimes overwriting old version with a new copy, > and sometimes a constant string assigned to path[], making it > impossible to release the resources properly: > > * A single dash "-" from the command line is a special signal that > the standard input is used for the side to be compared, and is > internally replaced with a copy of string "-" at a known address. > > * When run in a subdirectory, full paths to the two paths are > allocated and placed in path[]. > > * After the above happens, when comparing a file with a directory, > the directory side is replaced with the path to a file in the > directory with the same name as the file. > > This was perfectly fine for just two strings that are pathnames used > during the lifetime of the program and cleaned up upon program exit, > but it gets in the way when leak sanitizer is in effect. The third > step can be losing the full path that was allocated in the second > step, but it is not easy to tell if its input is an allocated piece > of memory to begin with. > > Loosen the earlier two steps a bit so that elements of the path[] > array that come to the directory/file comparison code are either the > singleton "-" or an allocated piece of memory. Use that knowledge > in the third step to release an allocated piece of memory when it > replaces the path to a directory with the path to a file in that > directory, and also at the end to release the two elements of the > path[] array as needed. > > Signed-off-by: Junio C Hamano <gitster@pobox.com> > --- > > * The previous one allowed strbuf_release() to free replacement.buf > which may be used in path[0] or path[1] potentially leading to > double freeing. The kosher way may be to use strbuf_detach() in > fixup_paths(), but this is a simpler fix, it is getting late in > the day, and I am getting sick of fighting the leak-checker, so... I wonder whether a much better way would be to first fix the code to always release `replacement`, like so: -- snip -- diff --git a/diff-no-index.c b/diff-no-index.c index 9a8b09346bd..87047605385 100644 --- a/diff-no-index.c +++ b/diff-no-index.c @@ -242,7 +242,7 @@ int diff_no_index(struct rev_info *revs, int implicit_no_index, int argc, const char **argv) { - int i, no_index; + int i, no_index, ret; const char *paths[2]; struct strbuf replacement = STRBUF_INIT; const char *prefix = revs->prefix; @@ -294,17 +294,23 @@ int diff_no_index(struct rev_info *revs, setup_diff_pager(&revs->diffopt); revs->diffopt.flags.exit_with_status = 1; - if (queue_diff(&revs->diffopt, paths[0], paths[1])) - return 1; + if (queue_diff(&revs->diffopt, paths[0], paths[1])) { + ret = 1; + goto out; + } + diff_set_mnemonic_prefix(&revs->diffopt, "1/", "2/"); diffcore_std(&revs->diffopt); diff_flush(&revs->diffopt); - strbuf_release(&replacement); - /* * The return code for --no-index imitates diff(1): * 0 = no changes, 1 = changes, else error */ - return diff_result_code(&revs->diffopt, 0); + ret = diff_result_code(&revs->diffopt, 0); + +out: + strbuf_release(&replacement); + + return ret; } -- snap -- After that, the proposed diff could be replaced by this diff: -- snip -- diff --git a/diff-no-index.c b/diff-no-index.c index 87047605385..d350e4381bc 100644 --- a/diff-no-index.c +++ b/diff-no-index.c @@ -244,6 +244,7 @@ int diff_no_index(struct rev_info *revs, { int i, no_index, ret; const char *paths[2]; + struct string_list to_release = STRING_LIST_INIT_DUP; struct strbuf replacement = STRBUF_INIT; const char *prefix = revs->prefix; struct option no_index_options[] = { @@ -274,6 +275,12 @@ int diff_no_index(struct rev_info *revs, p = file_from_standard_input; else if (prefix) p = prefix_filename(prefix, p); + else { + char *dup = xstrdup(p); + + p = dup; + string_list_append_nodup(&to_release, dup); + } paths[i] = p; } @@ -310,6 +317,7 @@ int diff_no_index(struct rev_info *revs, ret = diff_result_code(&revs->diffopt, 0); out: + string_list_clear(&to_release, 1); strbuf_release(&replacement); return ret; -- snap -- That approach has the distinct advantage of making it very easy to reason about the code. What do you think? Ciao, Dscho > > diff-no-index.c | 24 ++++++++++++++++++++++-- > 1 file changed, 22 insertions(+), 2 deletions(-) > > > diff --git a/diff-no-index.c b/diff-no-index.c > index 9a8b09346b..77a126469b 100644 > --- a/diff-no-index.c > +++ b/diff-no-index.c > @@ -208,6 +208,14 @@ static void append_basename(struct strbuf *path, const char *dir, const char *fi > strbuf_addstr(path, tail ? tail + 1 : file); > } > > +static void free_allocated_path(const char *path) > +{ > + if (!path || > + (path == file_from_standard_input)) > + return; > + free((char *)path); > +} > + > /* > * DWIM "diff D F" into "diff D/F F" and "diff F D" into "diff F D/F" > * Note that we append the basename of F to D/, so "diff a/b/file D" > @@ -226,9 +234,11 @@ static void fixup_paths(const char **path, struct strbuf *replacement) > return; > if (isdir0) { > append_basename(replacement, path[0], path[1]); > + free_allocated_path(path[0]); > path[0] = replacement->buf; > } else { > append_basename(replacement, path[1], path[0]); > + free_allocated_path(path[1]); > path[1] = replacement->buf; > } > } > @@ -274,6 +284,8 @@ int diff_no_index(struct rev_info *revs, > p = file_from_standard_input; > else if (prefix) > p = prefix_filename(prefix, p); > + else > + p = xstrdup(p); > paths[i] = p; > } > > @@ -294,13 +306,21 @@ int diff_no_index(struct rev_info *revs, > setup_diff_pager(&revs->diffopt); > revs->diffopt.flags.exit_with_status = 1; > > - if (queue_diff(&revs->diffopt, paths[0], paths[1])) > + if (queue_diff(&revs->diffopt, paths[0], paths[1])) { > + free_allocated_path(paths[0]); > + free_allocated_path(paths[1]); > return 1; > + } > diff_set_mnemonic_prefix(&revs->diffopt, "1/", "2/"); > diffcore_std(&revs->diffopt); > diff_flush(&revs->diffopt); > > - strbuf_release(&replacement); > + /* > + * do not strbuf_release(&replacement), as it is in paths[] > + * when replacement was actually used. > + */ > + free_allocated_path(paths[0]); > + free_allocated_path(paths[1]); > > /* > * The return code for --no-index imitates diff(1): > -- > 2.37.3-661-g73a641a77a > >
On Mon, Sep 05 2022, Johannes Schindelin wrote: > Hi Junio, > > On Fri, 2 Sep 2022, Junio C Hamano wrote: > >> "git diff --no-index" codepath starts with the two elements in >> argv[] and munges them into two paths to be compared, stored in a >> separate path[] arrays. The munging is implemented in a rather >> haphazard way, sometimes overwriting old version with a new copy, >> and sometimes a constant string assigned to path[], making it >> impossible to release the resources properly: >> >> * A single dash "-" from the command line is a special signal that >> the standard input is used for the side to be compared, and is >> internally replaced with a copy of string "-" at a known address. >> >> * When run in a subdirectory, full paths to the two paths are >> allocated and placed in path[]. >> >> * After the above happens, when comparing a file with a directory, >> the directory side is replaced with the path to a file in the >> directory with the same name as the file. >> >> This was perfectly fine for just two strings that are pathnames used >> during the lifetime of the program and cleaned up upon program exit, >> but it gets in the way when leak sanitizer is in effect. The third >> step can be losing the full path that was allocated in the second >> step, but it is not easy to tell if its input is an allocated piece >> of memory to begin with. >> >> Loosen the earlier two steps a bit so that elements of the path[] >> array that come to the directory/file comparison code are either the >> singleton "-" or an allocated piece of memory. Use that knowledge >> in the third step to release an allocated piece of memory when it >> replaces the path to a directory with the path to a file in that >> directory, and also at the end to release the two elements of the >> path[] array as needed. >> >> Signed-off-by: Junio C Hamano <gitster@pobox.com> >> --- >> >> * The previous one allowed strbuf_release() to free replacement.buf >> which may be used in path[0] or path[1] potentially leading to >> double freeing. The kosher way may be to use strbuf_detach() in >> fixup_paths(), but this is a simpler fix, it is getting late in >> the day, and I am getting sick of fighting the leak-checker, so... > > I wonder whether a much better way would be to first fix the code to > always release `replacement`, like so: > > -- snip -- > diff --git a/diff-no-index.c b/diff-no-index.c > index 9a8b09346bd..87047605385 100644 > --- a/diff-no-index.c > +++ b/diff-no-index.c > @@ -242,7 +242,7 @@ int diff_no_index(struct rev_info *revs, > int implicit_no_index, > int argc, const char **argv) > { > - int i, no_index; > + int i, no_index, ret; > const char *paths[2]; > struct strbuf replacement = STRBUF_INIT; > const char *prefix = revs->prefix; > @@ -294,17 +294,23 @@ int diff_no_index(struct rev_info *revs, > setup_diff_pager(&revs->diffopt); > revs->diffopt.flags.exit_with_status = 1; > > - if (queue_diff(&revs->diffopt, paths[0], paths[1])) > - return 1; > + if (queue_diff(&revs->diffopt, paths[0], paths[1])) { > + ret = 1; > + goto out; > + } > + > diff_set_mnemonic_prefix(&revs->diffopt, "1/", "2/"); > diffcore_std(&revs->diffopt); > diff_flush(&revs->diffopt); > > - strbuf_release(&replacement); > - > /* > * The return code for --no-index imitates diff(1): > * 0 = no changes, 1 = changes, else error > */ > - return diff_result_code(&revs->diffopt, 0); > + ret = diff_result_code(&revs->diffopt, 0); > + > +out: > + strbuf_release(&replacement); > + > + return ret; > } > -- snap -- > > After that, the proposed diff could be replaced by this diff: > > -- snip -- > diff --git a/diff-no-index.c b/diff-no-index.c > index 87047605385..d350e4381bc 100644 > --- a/diff-no-index.c > +++ b/diff-no-index.c > @@ -244,6 +244,7 @@ int diff_no_index(struct rev_info *revs, > { > int i, no_index, ret; > const char *paths[2]; > + struct string_list to_release = STRING_LIST_INIT_DUP; > struct strbuf replacement = STRBUF_INIT; > const char *prefix = revs->prefix; > struct option no_index_options[] = { > @@ -274,6 +275,12 @@ int diff_no_index(struct rev_info *revs, > p = file_from_standard_input; > else if (prefix) > p = prefix_filename(prefix, p); > + else { > + char *dup = xstrdup(p); > + > + p = dup; > + string_list_append_nodup(&to_release, dup); > + } > paths[i] = p; > } > > @@ -310,6 +317,7 @@ int diff_no_index(struct rev_info *revs, > ret = diff_result_code(&revs->diffopt, 0); > > out: > + string_list_clear(&to_release, 1); > strbuf_release(&replacement); > > return ret; > > -- snap -- > > That approach has the distinct advantage of making it very easy to reason > about the code. > > What do you think? > > Ciao, > Dscho > >> >> diff-no-index.c | 24 ++++++++++++++++++++++-- >> 1 file changed, 22 insertions(+), 2 deletions(-) >> >> >> diff --git a/diff-no-index.c b/diff-no-index.c >> index 9a8b09346b..77a126469b 100644 >> --- a/diff-no-index.c >> +++ b/diff-no-index.c >> @@ -208,6 +208,14 @@ static void append_basename(struct strbuf *path, const char *dir, const char *fi >> strbuf_addstr(path, tail ? tail + 1 : file); >> } >> >> +static void free_allocated_path(const char *path) >> +{ >> + if (!path || >> + (path == file_from_standard_input)) >> + return; >> + free((char *)path); >> +} >> + >> /* >> * DWIM "diff D F" into "diff D/F F" and "diff F D" into "diff F D/F" >> * Note that we append the basename of F to D/, so "diff a/b/file D" >> @@ -226,9 +234,11 @@ static void fixup_paths(const char **path, struct strbuf *replacement) >> return; >> if (isdir0) { >> append_basename(replacement, path[0], path[1]); >> + free_allocated_path(path[0]); >> path[0] = replacement->buf; >> } else { >> append_basename(replacement, path[1], path[0]); >> + free_allocated_path(path[1]); >> path[1] = replacement->buf; >> } >> } >> @@ -274,6 +284,8 @@ int diff_no_index(struct rev_info *revs, >> p = file_from_standard_input; >> else if (prefix) >> p = prefix_filename(prefix, p); >> + else >> + p = xstrdup(p); >> paths[i] = p; >> } >> >> @@ -294,13 +306,21 @@ int diff_no_index(struct rev_info *revs, >> setup_diff_pager(&revs->diffopt); >> revs->diffopt.flags.exit_with_status = 1; >> >> - if (queue_diff(&revs->diffopt, paths[0], paths[1])) >> + if (queue_diff(&revs->diffopt, paths[0], paths[1])) { >> + free_allocated_path(paths[0]); >> + free_allocated_path(paths[1]); >> return 1; >> + } >> diff_set_mnemonic_prefix(&revs->diffopt, "1/", "2/"); >> diffcore_std(&revs->diffopt); >> diff_flush(&revs->diffopt); >> >> - strbuf_release(&replacement); >> + /* >> + * do not strbuf_release(&replacement), as it is in paths[] >> + * when replacement was actually used. >> + */ >> + free_allocated_path(paths[0]); >> + free_allocated_path(paths[1]); >> >> /* >> * The return code for --no-index imitates diff(1): >> -- >> 2.37.3-661-g73a641a77a >> >> That looks like a much better approach, I'd think you'd want this on top, because: * We entirely avoid playing cames with the string_list "dup" and then "nodup" append. In some cases we have to, but in this case we can just get the pointer to the member we just created, and avoid the explicit xstrdup() in the caller. * The free_util=1 in your code isn't needed/is a bug, we make no use of "util" here, so it should be free_util=0 * It avoids the "add braces to all if/else arms" part of CodingGuidelines. diff --git a/diff-no-index.c b/diff-no-index.c index d350e4381bc..2861319c0e5 100644 --- a/diff-no-index.c +++ b/diff-no-index.c @@ -275,12 +275,8 @@ int diff_no_index(struct rev_info *revs, p = file_from_standard_input; else if (prefix) p = prefix_filename(prefix, p); - else { - char *dup = xstrdup(p); - - p = dup; - string_list_append_nodup(&to_release, dup); - } + else + p = string_list_append(&to_release, p)->string; paths[i] = p; } @@ -317,7 +313,7 @@ int diff_no_index(struct rev_info *revs, ret = diff_result_code(&revs->diffopt, 0); out: - string_list_clear(&to_release, 1); + string_list_clear(&to_release, 0); strbuf_release(&replacement); return ret;
René Scharfe <l.s.r@web.de> writes: > Am 03.09.22 um 01:49 schrieb Junio C Hamano: >> "git diff --no-index" codepath starts with the two elements in >> argv[] and munges them into two paths to be compared, stored in a >> separate path[] arrays. The munging is implemented in a rather >> haphazard way, sometimes overwriting old version with a new copy, >> and sometimes a constant string assigned to path[], making it >> impossible to release the resources properly: >> >> * A single dash "-" from the command line is a special signal that >> the standard input is used for the side to be compared, and is >> internally replaced with a copy of string "-" at a known address. >> >> * When run in a subdirectory, full paths to the two paths are >> allocated and placed in path[]. >> >> * After the above happens, when comparing a file with a directory, >> the directory side is replaced with the path to a file in the >> directory with the same name as the file. >> >> This was perfectly fine for just two strings that are pathnames used >> during the lifetime of the program and cleaned up upon program exit, >> but it gets in the way when leak sanitizer is in effect. The third >> step can be losing the full path that was allocated in the second >> step, but it is not easy to tell if its input is an allocated piece >> of memory to begin with. >> >> Loosen the earlier two steps a bit so that elements of the path[] >> array that come to the directory/file comparison code are either the >> singleton "-" or an allocated piece of memory. Use that knowledge >> in the third step to release an allocated piece of memory when it >> replaces the path to a directory with the path to a file in that >> directory, and also at the end to release the two elements of the >> path[] array as needed. >> >> Signed-off-by: Junio C Hamano <gitster@pobox.com> >> --- >> >> * The previous one allowed strbuf_release() to free replacement.buf >> which may be used in path[0] or path[1] potentially leading to >> double freeing. The kosher way may be to use strbuf_detach() in >> fixup_paths(), but this is a simpler fix, it is getting late in >> the day, and I am getting sick of fighting the leak-checker, so... >> >> diff-no-index.c | 24 ++++++++++++++++++++++-- >> 1 file changed, 22 insertions(+), 2 deletions(-) >> >> >> diff --git a/diff-no-index.c b/diff-no-index.c >> index 9a8b09346b..77a126469b 100644 >> --- a/diff-no-index.c >> +++ b/diff-no-index.c >> @@ -208,6 +208,14 @@ static void append_basename(struct strbuf *path, const char *dir, const char *fi >> strbuf_addstr(path, tail ? tail + 1 : file); >> } >> >> +static void free_allocated_path(const char *path) >> +{ >> + if (!path || > > How can path be NULL? And if it was, why shield free(3) from it? See the comment under three-dashes of the first iteration. >> + /* >> + * do not strbuf_release(&replacement), as it is in paths[] >> + * when replacement was actually used. >> + */ >> + free_allocated_path(paths[0]); >> + free_allocated_path(paths[1]); >> >> /* >> * The return code for --no-index imitates diff(1): > > Perhaps avoid the need for that comment by moving that strbuf to where > it's used and have it spend its full lifecycle there? Something like: Yup, that is what I said in the comment under three-dashes (with the reason why I didn't bother). Quite honestly I am sick of fighting the overzealous leak-checker so I'd very much appreciate if somebody else pick this up and run with it. Thanks.
Hi Ævar, On Mon, 5 Sep 2022, Ævar Arnfjörð Bjarmason wrote: > On Mon, Sep 05 2022, Johannes Schindelin wrote: > > [...] > > + string_list_clear(&to_release, 1); > [...] > > * The free_util=1 in your code isn't needed/is a bug, we make no use of > "util" here, so it should be free_util=0 Calling it a bug is a bit strong, and misses the reason why I did it: future-proofing. In any case, René took up Junio's ask and provided a new iteration that side-steps this concern altogether, therefore the point is now moot. Ciao, Johannes
On Wed, Sep 07 2022, Johannes Schindelin wrote: > Hi Ævar, > > On Mon, 5 Sep 2022, Ævar Arnfjörð Bjarmason wrote: > >> On Mon, Sep 05 2022, Johannes Schindelin wrote: >> >> [...] >> > + string_list_clear(&to_release, 1); >> [...] >> >> * The free_util=1 in your code isn't needed/is a bug, we make no use of >> "util" here, so it should be free_util=0 > > Calling it a bug is a bit strong[...] Yes, FWIW I meant that in the sense of "the author probably didn't mean this" or "it was copy/pasted", but it has no effect currently, as we'll always have NULL "util" members. > , and misses the reason why I did it: future-proofing. I didn't think it was intentional, but obviously you know better about the intent. "Future proofing" seems like a bad reason for that API use however. If you look at the various "util" users some of them want to free() it, and some don't. If you forget to free() the worst you'll have is a memory leak, but if you have some boilerplate free() there you'll probably get a segfault. Without knowing what the future code looks like we don't know whether it would make any sense to free() that util use. > In any case, René took up Junio's ask and provided a new iteration that > side-steps this concern altogether, therefore the point is now moot. Indeed, that patch LGTM.
diff --git a/diff-no-index.c b/diff-no-index.c index 9a8b09346b..77a126469b 100644 --- a/diff-no-index.c +++ b/diff-no-index.c @@ -208,6 +208,14 @@ static void append_basename(struct strbuf *path, const char *dir, const char *fi strbuf_addstr(path, tail ? tail + 1 : file); } +static void free_allocated_path(const char *path) +{ + if (!path || + (path == file_from_standard_input)) + return; + free((char *)path); +} + /* * DWIM "diff D F" into "diff D/F F" and "diff F D" into "diff F D/F" * Note that we append the basename of F to D/, so "diff a/b/file D" @@ -226,9 +234,11 @@ static void fixup_paths(const char **path, struct strbuf *replacement) return; if (isdir0) { append_basename(replacement, path[0], path[1]); + free_allocated_path(path[0]); path[0] = replacement->buf; } else { append_basename(replacement, path[1], path[0]); + free_allocated_path(path[1]); path[1] = replacement->buf; } } @@ -274,6 +284,8 @@ int diff_no_index(struct rev_info *revs, p = file_from_standard_input; else if (prefix) p = prefix_filename(prefix, p); + else + p = xstrdup(p); paths[i] = p; } @@ -294,13 +306,21 @@ int diff_no_index(struct rev_info *revs, setup_diff_pager(&revs->diffopt); revs->diffopt.flags.exit_with_status = 1; - if (queue_diff(&revs->diffopt, paths[0], paths[1])) + if (queue_diff(&revs->diffopt, paths[0], paths[1])) { + free_allocated_path(paths[0]); + free_allocated_path(paths[1]); return 1; + } diff_set_mnemonic_prefix(&revs->diffopt, "1/", "2/"); diffcore_std(&revs->diffopt); diff_flush(&revs->diffopt); - strbuf_release(&replacement); + /* + * do not strbuf_release(&replacement), as it is in paths[] + * when replacement was actually used. + */ + free_allocated_path(paths[0]); + free_allocated_path(paths[1]); /* * The return code for --no-index imitates diff(1):
"git diff --no-index" codepath starts with the two elements in argv[] and munges them into two paths to be compared, stored in a separate path[] arrays. The munging is implemented in a rather haphazard way, sometimes overwriting old version with a new copy, and sometimes a constant string assigned to path[], making it impossible to release the resources properly: * A single dash "-" from the command line is a special signal that the standard input is used for the side to be compared, and is internally replaced with a copy of string "-" at a known address. * When run in a subdirectory, full paths to the two paths are allocated and placed in path[]. * After the above happens, when comparing a file with a directory, the directory side is replaced with the path to a file in the directory with the same name as the file. This was perfectly fine for just two strings that are pathnames used during the lifetime of the program and cleaned up upon program exit, but it gets in the way when leak sanitizer is in effect. The third step can be losing the full path that was allocated in the second step, but it is not easy to tell if its input is an allocated piece of memory to begin with. Loosen the earlier two steps a bit so that elements of the path[] array that come to the directory/file comparison code are either the singleton "-" or an allocated piece of memory. Use that knowledge in the third step to release an allocated piece of memory when it replaces the path to a directory with the path to a file in that directory, and also at the end to release the two elements of the path[] array as needed. Signed-off-by: Junio C Hamano <gitster@pobox.com> --- * The previous one allowed strbuf_release() to free replacement.buf which may be used in path[0] or path[1] potentially leading to double freeing. The kosher way may be to use strbuf_detach() in fixup_paths(), but this is a simpler fix, it is getting late in the day, and I am getting sick of fighting the leak-checker, so... diff-no-index.c | 24 ++++++++++++++++++++++-- 1 file changed, 22 insertions(+), 2 deletions(-)