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kpatch-elf: fix the unexpected elf classes

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kpatch-elf::kpatch_write_output_elf will call the gelf_getclass()
to acquire the output elf's class. But the input parameter kelf->elf
is NULL, the gelf_getclass(kelf->elf) will return ELFCLASSNONE, not
the value we expect ELFCLASS32 or ELFCLASS64.

the gelf_getclass function code:
int
gelf_getclass (Elf *elf)
{
  return elf == NULL || elf->kind != ELF_K_ELF ? ELFCLASSNONE : elf->class;
}

the gelf_newehdr fuction code:
void *
gelf_newehdr (Elf *elf, int class)
{
  return (class == ELFCLASS32
          ? (void *) INTUSE(elf32_newehdr) (elf)
          : (void *) INTUSE(elf64_newehdr) (elf));
}

Luckily, when we create a patch for x86_64 or powerpc64, if we pass the
ELFCLASSNONE for the function gelf_newehdr, it will return elf64_newehdr,
so don't cause the fault. But it's better to use the gelf_getclass(elf)
instead of gelf_getclass(kelf->elf).

Signed-off-by: chenzefeng <chenzefeng2@huawei.com>
This commit is contained in:
chenzefeng 2019-05-12 09:58:22 +08:00
parent bfe1c74d4f
commit 3bfc85732d
1 changed files with 1 additions and 1 deletions
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2
kpatch-build/kpatch-elf.c
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@ -765,7 +765,7 @@ void kpatch_write_output_elf(struct kpatch_elf *kelf, Elf *elf, char *outfile)
if (!elfout)
ERROR("elf_begin");
if (!gelf_newehdr(elfout, gelf_getclass(kelf->elf)))
if (!gelf_newehdr(elfout, gelf_getclass(elf)))
ERROR("gelf_newehdr");
if (!gelf_getehdr(elfout, &ehout))