On Sat, Nov 10, 2018 at 01:18:36PM +0100, Artem Savkov wrote: > On Fri, Nov 09, 2018 at 11:23:09AM -0600, Josh Poimboeuf wrote: > > On Wed, Nov 07, 2018 at 10:45:15PM +0100, Artem Savkov wrote: > > > Because find_symbol_by_name() traverses the same lists as read_symbols() > > > changing sym->name in place without copying it affects the result of > > > find_symbol_by_name() and, in case when ".cold" function precedes it's > > > parent in sec->symbol_list, can result in function being considered a > > > parent of itself. This leads to function length being set to 0 and other > > > consequent side-effects including a segfault in add_switch_table(). > > > The effects of this bug are only visible when building with > > > -ffunction-sections in KCFLAGS. > > > > > > Fix by copying the search string instead of modifying it in place. > > > > > > Signed-off-by: Artem Savkov <asav...@redhat.com> > > > > This needs a "Fixes" tag to identify the patch which introduced the bug. > > Ok, will do. > > > > --- > > > tools/objtool/elf.c | 7 ++++--- > > > 1 file changed, 4 insertions(+), 3 deletions(-) > > > > > > diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c > > > index 6dbb9fae0f9d..781c8afb29b9 100644 > > > --- a/tools/objtool/elf.c > > > +++ b/tools/objtool/elf.c > > > @@ -298,6 +298,7 @@ static int read_symbols(struct elf *elf) > > > /* Create parent/child links for any cold subfunctions */ > > > list_for_each_entry(sec, &elf->sections, list) { > > > list_for_each_entry(sym, &sec->symbol_list, list) { > > > + char *pname; > > > if (sym->type != STT_FUNC) > > > continue; > > > sym->pfunc = sym->cfunc = sym; > > > @@ -305,9 +306,9 @@ static int read_symbols(struct elf *elf) > > > if (!coldstr) > > > continue; > > > > > > - coldstr[0] = '\0'; > > > - pfunc = find_symbol_by_name(elf, sym->name); > > > - coldstr[0] = '.'; > > > + pname = strndup(sym->name, coldstr - sym->name); > > > + pfunc = find_symbol_by_name(elf, pname); > > > + free(pname); > > > > > > if (!pfunc) { > > > WARN("%s(): can't find parent function", > > > > strndup()'s return code needs to be checked. > > > > Also, for such a short-lived allocation, I think a stack-allocated > > string would be better. > > Hm, there seems to be no limit on lengths of strings in string table. > What size would you consider reasonable for this stack-allocated string?
I think it's fine to pick a reasonable maximum (128?) and then verify the string fits in the array before copying it. -- Josh