| Message ID | 1520970663-19633-1-git-send-email-s.mesoraca16@gmail.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
On Tue, Mar 13, 2018 at 12:51 PM, Salvatore Mesoraca <s.mesoraca16@gmail.com> wrote: > Avoid a VLA[1] by using a real constant expression instead of a variable. > The compiler should be able to optimize the original code and avoid using > an actual VLA. Anyway this change is useful because it will avoid a false > positive with -Wvla, it might also help the compiler generating better > code. > > [1] https://lkml.org/lkml/2018/3/7/621 > > Signed-off-by: Salvatore Mesoraca <s.mesoraca16@gmail.com> > --- > kernel/trace/ftrace.c | 7 +++---- > 1 file changed, 3 insertions(+), 4 deletions(-) > > diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c > index eac9ce2..adebb92 100644 > --- a/kernel/trace/ftrace.c > +++ b/kernel/trace/ftrace.c > @@ -3902,14 +3902,13 @@ static bool module_exists(const char *module) > { > /* All modules have the symbol __this_module */ > const char this_mod[] = "__this_module"; > - const int modname_size = MAX_PARAM_PREFIX_LEN + sizeof(this_mod) + 1; > - char modname[modname_size + 1]; > + char modname[MAX_PARAM_PREFIX_LEN + sizeof(this_mod) + 1]; Actually, I think this needs to be "+ 2" (":" and NULL). > unsigned long val; > int n; > > - n = snprintf(modname, modname_size + 1, "%s:%s", module, this_mod); > + n = snprintf(modname, sizeof(modname), "%s:%s", module, this_mod); > > - if (n > modname_size) > + if (n > sizeof(modname) - 1) > return false; > > val = module_kallsyms_lookup_name(modname); Otherwise, looks good! -Kees
2018-03-27 1:16 GMT+02:00 Kees Cook <keescook@chromium.org>: > On Tue, Mar 13, 2018 at 12:51 PM, Salvatore Mesoraca > <s.mesoraca16@gmail.com> wrote: >> Avoid a VLA[1] by using a real constant expression instead of a variable. >> The compiler should be able to optimize the original code and avoid using >> an actual VLA. Anyway this change is useful because it will avoid a false >> positive with -Wvla, it might also help the compiler generating better >> code. >> >> [1] https://lkml.org/lkml/2018/3/7/621 >> >> Signed-off-by: Salvatore Mesoraca <s.mesoraca16@gmail.com> >> --- >> kernel/trace/ftrace.c | 7 +++---- >> 1 file changed, 3 insertions(+), 4 deletions(-) >> >> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c >> index eac9ce2..adebb92 100644 >> --- a/kernel/trace/ftrace.c >> +++ b/kernel/trace/ftrace.c >> @@ -3902,14 +3902,13 @@ static bool module_exists(const char *module) >> { >> /* All modules have the symbol __this_module */ >> const char this_mod[] = "__this_module"; >> - const int modname_size = MAX_PARAM_PREFIX_LEN + sizeof(this_mod) + 1; >> - char modname[modname_size + 1]; >> + char modname[MAX_PARAM_PREFIX_LEN + sizeof(this_mod) + 1]; > > Actually, I think this needs to be "+ 2" (":" and NULL). Ah, right! I'll fix it ASAP :) > >> unsigned long val; >> int n; >> >> - n = snprintf(modname, modname_size + 1, "%s:%s", module, this_mod); >> + n = snprintf(modname, sizeof(modname), "%s:%s", module, this_mod); >> >> - if (n > modname_size) >> + if (n > sizeof(modname) - 1) >> return false; >> >> val = module_kallsyms_lookup_name(modname); > > Otherwise, looks good! Thank you! Salvatore
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index eac9ce2..adebb92 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -3902,14 +3902,13 @@ static bool module_exists(const char *module) { /* All modules have the symbol __this_module */ const char this_mod[] = "__this_module"; - const int modname_size = MAX_PARAM_PREFIX_LEN + sizeof(this_mod) + 1; - char modname[modname_size + 1]; + char modname[MAX_PARAM_PREFIX_LEN + sizeof(this_mod) + 1]; unsigned long val; int n; - n = snprintf(modname, modname_size + 1, "%s:%s", module, this_mod); + n = snprintf(modname, sizeof(modname), "%s:%s", module, this_mod); - if (n > modname_size) + if (n > sizeof(modname) - 1) return false; val = module_kallsyms_lookup_name(modname);
Avoid a VLA[1] by using a real constant expression instead of a variable. The compiler should be able to optimize the original code and avoid using an actual VLA. Anyway this change is useful because it will avoid a false positive with -Wvla, it might also help the compiler generating better code. [1] https://lkml.org/lkml/2018/3/7/621 Signed-off-by: Salvatore Mesoraca <s.mesoraca16@gmail.com> --- kernel/trace/ftrace.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-)