| Message ID | 20200208073607.21229-1-plautrba@redhat.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [v3] libselinux: Eliminate use of security_compute_user() | expand |
On 2/8/20 2:36 AM, Petr Lautrbach wrote: > get_ordered_context_list() code used to ask the kernel to compute the complete > set of reachable contexts using /sys/fs/selinux/user aka > security_compute_user(). This set can be so huge so that it doesn't fit into a > kernel page and security_compute_user() fails. Even if it doesn't fail, > get_ordered_context_list() throws away the vast majority of the returned > contexts because they don't match anything in > /etc/selinux/targeted/contexts/default_contexts or > /etc/selinux/targeted/contexts/users/ > > get_ordered_context_list() is rewritten to compute set of contexts based on > /etc/selinux/targeted/contexts/users/ and > /etc/selinux/targeted/contexts/default_contexts files and to return only valid > contexts, using security_check_context(), from this set. > > Fixes: https://github.com/SELinuxProject/selinux/issues/28 > > Signed-off-by: Petr Lautrbach <plautrba@redhat.com> > --- > diff --git a/libselinux/src/get_context_list.c b/libselinux/src/get_context_list.c > index 689e46589f30..cc39f8c6a96c 100644 > --- a/libselinux/src/get_context_list.c > +++ b/libselinux/src/get_context_list.c > @@ -243,23 +222,89 @@ static int get_context_order(FILE * fp, > if (*end) > *end++ = 0; > > - /* Check for a match in the reachable list. */ > - rc = find_partialcon(reachable, nreach, start); > - if (rc < 0) { > - /* No match, skip it. */ > + /* Check whether a new context is valid */ > + if (SIZE_MAX - user_len < strlen(start) + 1) { > + fprintf(stderr, "%s: one of partial contexts is too big\n", __FUNCTION__); > + errno = EINVAL; > + rc = -1; > + goto out; > + } > + usercon_len = user_len + strlen(start) + 1; > + usercon_str = malloc(usercon_len); > + if (!usercon_str) { > + rc = -1; > + goto out; > + } > + > + /* set range from fromcon in the new usercon */ > + snprintf(usercon_str, usercon_len - 1, "%s:%s", user, start); > + usercon = context_new(usercon_str); > + if (!usercon) { > + if (errno != EINVAL) { > + free(usercon_str); > + rc = -1; > + goto out; > + } > + fprintf(stderr, > + "%s: can't create a context from %s, skipping\n", > + __FUNCTION__, usercon_str); > + free(usercon_str); > + start = end; > + continue; > + } > + if (context_range_set(usercon, fromlevel) != 0) { > + if (errno != EINVAL) { > + free(usercon_str); > + rc = -1; > + goto out; > + } > + fprintf(stderr, > + "%s: can't set a new range %s for %s, skipping\n", > + __FUNCTION__, fromlevel, usercon_str); > + free(usercon_str); I'd think we could always treat this as a fatal error but up to you. Regardless, we need to also do a context_free(usercon); here or we will leak the memory. > start = end; > continue; > } > + free(usercon_str); > + usercon_str = context_str(usercon); > + if (!usercon_str) { > + rc = -1; context_free(usercon); needed here as well. > + goto out; > + } > > - /* If a match is found and the entry is not already ordered > - (e.g. due to prior match in prior config file), then set > - the ordering for it. */ > - i = rc; > - if (ordering[i] == nreach) > - ordering[i] = (*nordered)++; > + /* check whether usercon is already in reachable */ > + if (is_in_reachable(*reachable, usercon_str)) { > + start = end; And again. > + continue; > + } > + if (security_check_context(usercon_str) == 0) { > + if (*nreachable == 0) { > + new_reachable = malloc(2 * sizeof(char *)); > + if (!new_reachable) { > + context_free(usercon); > + rc = -1; > + goto out; > + } > + } else { > + new_reachable = realloc(*reachable, (*nreachable + 2) * sizeof(char *)); > + if (!new_reachable) { > + context_free(usercon); > + rc = -1; > + goto out; > + } > + } > + new_reachable[*nreachable] = strdup(usercon_str); > + if (new_reachable[*nreachable] == NULL) { > + rc = -1; > + goto out; > + } > + new_reachable[*nreachable + 1] = 0; > + *reachable = new_reachable; > + *nreachable += 1; > + } > + context_free(usercon); > start = end; > } > - > rc = 0; > > out:
I haven't looked at the whole patch properly yet, but noting what I found so far (see below)... On Sat, Feb 8, 2020 at 8:36 AM Petr Lautrbach <plautrba@redhat.com> wrote: > get_ordered_context_list() code used to ask the kernel to compute the complete > set of reachable contexts using /sys/fs/selinux/user aka > security_compute_user(). This set can be so huge so that it doesn't fit into a > kernel page and security_compute_user() fails. Even if it doesn't fail, > get_ordered_context_list() throws away the vast majority of the returned > contexts because they don't match anything in > /etc/selinux/targeted/contexts/default_contexts or > /etc/selinux/targeted/contexts/users/ > > get_ordered_context_list() is rewritten to compute set of contexts based on > /etc/selinux/targeted/contexts/users/ and > /etc/selinux/targeted/contexts/default_contexts files and to return only valid > contexts, using security_check_context(), from this set. > > Fixes: https://github.com/SELinuxProject/selinux/issues/28 > > Signed-off-by: Petr Lautrbach <plautrba@redhat.com> > --- > > v3 changes: > > - check return values of context_range_set() and context_str() > - do not add duplicate entries to reachable contexts > > > libselinux/src/get_context_list.c | 219 ++++++++++++++---------------- > 1 file changed, 103 insertions(+), 116 deletions(-) > > diff --git a/libselinux/src/get_context_list.c b/libselinux/src/get_context_list.c > index 689e46589f30..cc39f8c6a96c 100644 > --- a/libselinux/src/get_context_list.c > +++ b/libselinux/src/get_context_list.c <snip> > -static int get_context_order(FILE * fp, > +static int get_context_user(FILE * fp, > char * fromcon, > - char ** reachable, > - unsigned int nreach, > - unsigned int *ordering, unsigned int *nordered) > + const char * user, > + char ***reachable, > + unsigned int *nreachable) > { > char *start, *end = NULL; > char *line = NULL; > - size_t line_len = 0; > + size_t line_len = 0, usercon_len; > + size_t user_len = strlen(user); > ssize_t len; > int found = 0; > - const char *fromrole, *fromtype; > + const char *fromrole, *fromtype, *fromlevel; > char *linerole, *linetype; > - unsigned int i; > + char **new_reachable = NULL; > + char *usercon_str; > context_t con; > + context_t usercon; > + > int rc; > > errno = -EINVAL; > @@ -180,6 +158,7 @@ static int get_context_order(FILE * fp, > return -1; > fromrole = context_role_get(con); > fromtype = context_type_get(con); > + fromlevel = context_range_get(con); > if (!fromrole || !fromtype) { > context_free(con); > return -1; > @@ -243,23 +222,89 @@ static int get_context_order(FILE * fp, > if (*end) > *end++ = 0; > > - /* Check for a match in the reachable list. */ > - rc = find_partialcon(reachable, nreach, start); > - if (rc < 0) { > - /* No match, skip it. */ > + /* Check whether a new context is valid */ > + if (SIZE_MAX - user_len < strlen(start) + 1) { You need to also account for either the null character or the colon (not sure which one you missed). > + fprintf(stderr, "%s: one of partial contexts is too big\n", __FUNCTION__); > + errno = EINVAL; > + rc = -1; > + goto out; > + } > + usercon_len = user_len + strlen(start) + 1; > + usercon_str = malloc(usercon_len); Again, you are not accounting for one of '\0' or ':' here. > + if (!usercon_str) { > + rc = -1; > + goto out; > + } > + > + /* set range from fromcon in the new usercon */ > + snprintf(usercon_str, usercon_len - 1, "%s:%s", user, start); The second argument should be just usercon_len (assuming you fix the above) - see snprintf(3): "The functions snprintf() and vsnprintf() write at most size bytes (including the terminating null byte ('\0')) to str." So this should always result in a string with 2 last characters truncated (followed by a null character and an unused byte). Or am I missing something? Did you get correct strings when you tested this? <snip>
On 2/10/20 10:00 AM, Ondrej Mosnacek wrote: > I haven't looked at the whole patch properly yet, but noting what I > found so far (see below)... > > On Sat, Feb 8, 2020 at 8:36 AM Petr Lautrbach <plautrba@redhat.com> wrote: >> get_ordered_context_list() code used to ask the kernel to compute the complete >> set of reachable contexts using /sys/fs/selinux/user aka >> security_compute_user(). This set can be so huge so that it doesn't fit into a >> kernel page and security_compute_user() fails. Even if it doesn't fail, >> get_ordered_context_list() throws away the vast majority of the returned >> contexts because they don't match anything in >> /etc/selinux/targeted/contexts/default_contexts or >> /etc/selinux/targeted/contexts/users/ >> >> get_ordered_context_list() is rewritten to compute set of contexts based on >> /etc/selinux/targeted/contexts/users/ and >> /etc/selinux/targeted/contexts/default_contexts files and to return only valid >> contexts, using security_check_context(), from this set. >> >> Fixes: https://github.com/SELinuxProject/selinux/issues/28 >> >> Signed-off-by: Petr Lautrbach <plautrba@redhat.com> >> --- >> >> v3 changes: >> >> - check return values of context_range_set() and context_str() >> - do not add duplicate entries to reachable contexts >> >> >> libselinux/src/get_context_list.c | 219 ++++++++++++++---------------- >> 1 file changed, 103 insertions(+), 116 deletions(-) >> >> diff --git a/libselinux/src/get_context_list.c b/libselinux/src/get_context_list.c >> index 689e46589f30..cc39f8c6a96c 100644 >> --- a/libselinux/src/get_context_list.c >> +++ b/libselinux/src/get_context_list.c > > <snip> > >> -static int get_context_order(FILE * fp, >> +static int get_context_user(FILE * fp, >> char * fromcon, >> - char ** reachable, >> - unsigned int nreach, >> - unsigned int *ordering, unsigned int *nordered) >> + const char * user, >> + char ***reachable, >> + unsigned int *nreachable) >> { >> char *start, *end = NULL; >> char *line = NULL; >> - size_t line_len = 0; >> + size_t line_len = 0, usercon_len; >> + size_t user_len = strlen(user); >> ssize_t len; >> int found = 0; >> - const char *fromrole, *fromtype; >> + const char *fromrole, *fromtype, *fromlevel; >> char *linerole, *linetype; >> - unsigned int i; >> + char **new_reachable = NULL; >> + char *usercon_str; >> context_t con; >> + context_t usercon; >> + >> int rc; >> >> errno = -EINVAL; >> @@ -180,6 +158,7 @@ static int get_context_order(FILE * fp, >> return -1; >> fromrole = context_role_get(con); >> fromtype = context_type_get(con); >> + fromlevel = context_range_get(con); >> if (!fromrole || !fromtype) { >> context_free(con); >> return -1; >> @@ -243,23 +222,89 @@ static int get_context_order(FILE * fp, >> if (*end) >> *end++ = 0; >> >> - /* Check for a match in the reachable list. */ >> - rc = find_partialcon(reachable, nreach, start); >> - if (rc < 0) { >> - /* No match, skip it. */ >> + /* Check whether a new context is valid */ >> + if (SIZE_MAX - user_len < strlen(start) + 1) { > > You need to also account for either the null character or the colon > (not sure which one you missed). > >> + fprintf(stderr, "%s: one of partial contexts is too big\n", __FUNCTION__); >> + errno = EINVAL; >> + rc = -1; >> + goto out; >> + } >> + usercon_len = user_len + strlen(start) + 1; >> + usercon_str = malloc(usercon_len); > > Again, you are not accounting for one of '\0' or ':' here. > >> + if (!usercon_str) { >> + rc = -1; >> + goto out; >> + } >> + >> + /* set range from fromcon in the new usercon */ >> + snprintf(usercon_str, usercon_len - 1, "%s:%s", user, start); > > The second argument should be just usercon_len (assuming you fix the > above) - see snprintf(3): > > "The functions snprintf() and vsnprintf() write at most size bytes > (including the terminating null byte ('\0')) to str." > > So this should always result in a string with 2 last characters > truncated (followed by a null character and an unused byte). Or am I > missing something? Did you get correct strings when you tested this? It is truncating the "s0" level from start but then we are explicitly overriding the level via context_range_set(), so the bug gets masked.
diff --git a/libselinux/src/get_context_list.c b/libselinux/src/get_context_list.c index 689e46589f30..cc39f8c6a96c 100644 --- a/libselinux/src/get_context_list.c +++ b/libselinux/src/get_context_list.c @@ -2,6 +2,7 @@ #include <errno.h> #include <stdio.h> #include <stdio_ext.h> +#include <stdint.h> #include <stdlib.h> #include <string.h> #include <ctype.h> @@ -114,61 +115,38 @@ int get_default_context(const char *user, return 0; } -static int find_partialcon(char ** list, - unsigned int nreach, char *part) +static int is_in_reachable(char **reachable, const char *usercon_str) { - const char *conrole, *contype; - char *partrole, *parttype, *ptr; - context_t con; - unsigned int i; + if (!reachable) + return 0; - partrole = part; - ptr = part; - while (*ptr && !isspace(*ptr) && *ptr != ':') - ptr++; - if (*ptr != ':') - return -1; - *ptr++ = 0; - parttype = ptr; - while (*ptr && !isspace(*ptr) && *ptr != ':') - ptr++; - *ptr = 0; - - for (i = 0; i < nreach; i++) { - con = context_new(list[i]); - if (!con) - return -1; - conrole = context_role_get(con); - contype = context_type_get(con); - if (!conrole || !contype) { - context_free(con); - return -1; - } - if (!strcmp(conrole, partrole) && !strcmp(contype, parttype)) { - context_free(con); - return i; + for (; *reachable != NULL; reachable++) { + if (strcmp(*reachable, usercon_str) == 0) { + return 1; } - context_free(con); } - - return -1; + return 0; } -static int get_context_order(FILE * fp, +static int get_context_user(FILE * fp, char * fromcon, - char ** reachable, - unsigned int nreach, - unsigned int *ordering, unsigned int *nordered) + const char * user, + char ***reachable, + unsigned int *nreachable) { char *start, *end = NULL; char *line = NULL; - size_t line_len = 0; + size_t line_len = 0, usercon_len; + size_t user_len = strlen(user); ssize_t len; int found = 0; - const char *fromrole, *fromtype; + const char *fromrole, *fromtype, *fromlevel; char *linerole, *linetype; - unsigned int i; + char **new_reachable = NULL; + char *usercon_str; context_t con; + context_t usercon; + int rc; errno = -EINVAL; @@ -180,6 +158,7 @@ static int get_context_order(FILE * fp, return -1; fromrole = context_role_get(con); fromtype = context_type_get(con); + fromlevel = context_range_get(con); if (!fromrole || !fromtype) { context_free(con); return -1; @@ -243,23 +222,89 @@ static int get_context_order(FILE * fp, if (*end) *end++ = 0; - /* Check for a match in the reachable list. */ - rc = find_partialcon(reachable, nreach, start); - if (rc < 0) { - /* No match, skip it. */ + /* Check whether a new context is valid */ + if (SIZE_MAX - user_len < strlen(start) + 1) { + fprintf(stderr, "%s: one of partial contexts is too big\n", __FUNCTION__); + errno = EINVAL; + rc = -1; + goto out; + } + usercon_len = user_len + strlen(start) + 1; + usercon_str = malloc(usercon_len); + if (!usercon_str) { + rc = -1; + goto out; + } + + /* set range from fromcon in the new usercon */ + snprintf(usercon_str, usercon_len - 1, "%s:%s", user, start); + usercon = context_new(usercon_str); + if (!usercon) { + if (errno != EINVAL) { + free(usercon_str); + rc = -1; + goto out; + } + fprintf(stderr, + "%s: can't create a context from %s, skipping\n", + __FUNCTION__, usercon_str); + free(usercon_str); + start = end; + continue; + } + if (context_range_set(usercon, fromlevel) != 0) { + if (errno != EINVAL) { + free(usercon_str); + rc = -1; + goto out; + } + fprintf(stderr, + "%s: can't set a new range %s for %s, skipping\n", + __FUNCTION__, fromlevel, usercon_str); + free(usercon_str); start = end; continue; } + free(usercon_str); + usercon_str = context_str(usercon); + if (!usercon_str) { + rc = -1; + goto out; + } - /* If a match is found and the entry is not already ordered - (e.g. due to prior match in prior config file), then set - the ordering for it. */ - i = rc; - if (ordering[i] == nreach) - ordering[i] = (*nordered)++; + /* check whether usercon is already in reachable */ + if (is_in_reachable(*reachable, usercon_str)) { + start = end; + continue; + } + if (security_check_context(usercon_str) == 0) { + if (*nreachable == 0) { + new_reachable = malloc(2 * sizeof(char *)); + if (!new_reachable) { + context_free(usercon); + rc = -1; + goto out; + } + } else { + new_reachable = realloc(*reachable, (*nreachable + 2) * sizeof(char *)); + if (!new_reachable) { + context_free(usercon); + rc = -1; + goto out; + } + } + new_reachable[*nreachable] = strdup(usercon_str); + if (new_reachable[*nreachable] == NULL) { + rc = -1; + goto out; + } + new_reachable[*nreachable + 1] = 0; + *reachable = new_reachable; + *nreachable += 1; + } + context_free(usercon); start = end; } - rc = 0; out: @@ -313,21 +358,6 @@ static int get_failsafe_context(const char *user, char ** newcon) return 0; } -struct context_order { - char * con; - unsigned int order; -}; - -static int order_compare(const void *A, const void *B) -{ - const struct context_order *c1 = A, *c2 = B; - if (c1->order < c2->order) - return -1; - else if (c1->order > c2->order) - return 1; - return strcmp(c1->con, c2->con); -} - int get_ordered_context_list_with_level(const char *user, const char *level, char * fromcon, @@ -395,11 +425,8 @@ int get_ordered_context_list(const char *user, char *** list) { char **reachable = NULL; - unsigned int *ordering = NULL; - struct context_order *co = NULL; - char **ptr; int rc = 0; - unsigned int nreach = 0, nordered = 0, freefrom = 0, i; + unsigned nreachable = 0, freefrom = 0; FILE *fp; char *fname = NULL; size_t fname_len; @@ -413,23 +440,6 @@ int get_ordered_context_list(const char *user, freefrom = 1; } - /* Determine the set of reachable contexts for the user. */ - rc = security_compute_user(fromcon, user, &reachable); - if (rc < 0) - goto failsafe; - nreach = 0; - for (ptr = reachable; *ptr; ptr++) - nreach++; - if (!nreach) - goto failsafe; - - /* Initialize ordering array. */ - ordering = malloc(nreach * sizeof(unsigned int)); - if (!ordering) - goto failsafe; - for (i = 0; i < nreach; i++) - ordering[i] = nreach; - /* Determine the ordering to apply from the optional per-user config and from the global config. */ fname_len = strlen(user_contexts_path) + strlen(user) + 2; @@ -440,8 +450,8 @@ int get_ordered_context_list(const char *user, fp = fopen(fname, "re"); if (fp) { __fsetlocking(fp, FSETLOCKING_BYCALLER); - rc = get_context_order(fp, fromcon, reachable, nreach, ordering, - &nordered); + rc = get_context_user(fp, fromcon, user, &reachable, &nreachable); + fclose(fp); if (rc < 0 && errno != ENOENT) { fprintf(stderr, @@ -454,8 +464,7 @@ int get_ordered_context_list(const char *user, fp = fopen(selinux_default_context_path(), "re"); if (fp) { __fsetlocking(fp, FSETLOCKING_BYCALLER); - rc = get_context_order(fp, fromcon, reachable, nreach, ordering, - &nordered); + rc = get_context_user(fp, fromcon, user, &reachable, &nreachable); fclose(fp); if (rc < 0 && errno != ENOENT) { fprintf(stderr, @@ -463,32 +472,11 @@ int get_ordered_context_list(const char *user, __FUNCTION__, selinux_default_context_path()); /* Fall through */ } - rc = 0; + rc = nreachable; } - if (!nordered) - goto failsafe; - - /* Apply the ordering. */ - co = malloc(nreach * sizeof(struct context_order)); - if (!co) + if (!nreachable) goto failsafe; - for (i = 0; i < nreach; i++) { - co[i].con = reachable[i]; - co[i].order = ordering[i]; - } - qsort(co, nreach, sizeof(struct context_order), order_compare); - for (i = 0; i < nreach; i++) - reachable[i] = co[i].con; - free(co); - - /* Only report the ordered entries to the caller. */ - if (nordered <= nreach) { - for (i = nordered; i < nreach; i++) - free(reachable[i]); - reachable[nordered] = NULL; - rc = nordered; - } out: if (rc > 0) @@ -496,7 +484,6 @@ int get_ordered_context_list(const char *user, else freeconary(reachable); - free(ordering); if (freefrom) freecon(fromcon);
get_ordered_context_list() code used to ask the kernel to compute the complete set of reachable contexts using /sys/fs/selinux/user aka security_compute_user(). This set can be so huge so that it doesn't fit into a kernel page and security_compute_user() fails. Even if it doesn't fail, get_ordered_context_list() throws away the vast majority of the returned contexts because they don't match anything in /etc/selinux/targeted/contexts/default_contexts or /etc/selinux/targeted/contexts/users/ get_ordered_context_list() is rewritten to compute set of contexts based on /etc/selinux/targeted/contexts/users/ and /etc/selinux/targeted/contexts/default_contexts files and to return only valid contexts, using security_check_context(), from this set. Fixes: https://github.com/SELinuxProject/selinux/issues/28 Signed-off-by: Petr Lautrbach <plautrba@redhat.com> --- v3 changes: - check return values of context_range_set() and context_str() - do not add duplicate entries to reachable contexts libselinux/src/get_context_list.c | 219 ++++++++++++++---------------- 1 file changed, 103 insertions(+), 116 deletions(-)