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| author | Tobias Stoeckmann <tobias@stoeckmann.org> | 2015-02-10 19:46:40 +0100 |
|---|---|---|
| committer | Lucas De Marchi <lucas.demarchi@intel.com> | 2015-02-17 14:10:31 -0200 |
| commit | 249dc5909b09db72cc8958b382d8393235b70afd (patch) | |
| tree | 7608692e3a76c1bd7f303abd0e9b0678d8a3b5ab /libkmod | |
| parent | 246d67d493510df1547260d968937f4984f148e0 (diff) | |
| download | kmod-249dc5909b09db72cc8958b382d8393235b70afd.tar.gz kmod-249dc5909b09db72cc8958b382d8393235b70afd.tar.bz2 kmod-249dc5909b09db72cc8958b382d8393235b70afd.zip | |
libkmod: properly validate file size
In function kmod_elf_new, the file size has to be properly validated against
section offset. Currently, the file size is considered valid based on
ELF header size + section header size * section count. That is not sufficient.
In fact, ELF specifies a section header offset, which doesn't have to be the
size of the ELF header. The supplied test cases even cover this.
The correct test is: section offset + section header size * section count
This patch also verifies that this value won't overflow. I don't know a way
to crash a tool due to this bug, because later on the offset check would
prevent out-of-bounds access. An overflow would just mean to access a wrong
part in elf->memory. Yet it's a validation error.
Please note: The file size does not have to be validated against the size
of the ELF header again, elf_identify did this already.
Diffstat (limited to 'libkmod')
| -rw-r--r-- | libkmod/libkmod-elf.c | 10 |
1 files changed, 5 insertions, 5 deletions
diff --git a/libkmod/libkmod-elf.c b/libkmod/libkmod-elf.c index 4af829e..2f50ad2 100644 --- a/libkmod/libkmod-elf.c +++ b/libkmod/libkmod-elf.c @@ -272,7 +272,8 @@ static const char *elf_get_strings_section(const struct kmod_elf *elf, uint64_t struct kmod_elf *kmod_elf_new(const void *memory, off_t size) { struct kmod_elf *elf; - size_t hdr_size, shdr_size, min_size; + uint64_t min_size; + size_t shdrs_size, shdr_size; int class; assert_cc(sizeof(uint16_t) == sizeof(Elf32_Half)); @@ -308,12 +309,10 @@ struct kmod_elf *kmod_elf_new(const void *memory, off_t size) if (elf->class & KMOD_ELF_32) { const Elf32_Ehdr *hdr _unused_ = elf_get_mem(elf, 0); LOAD_HEADER; - hdr_size = sizeof(Elf32_Ehdr); shdr_size = sizeof(Elf32_Shdr); } else { const Elf64_Ehdr *hdr _unused_ = elf_get_mem(elf, 0); LOAD_HEADER; - hdr_size = sizeof(Elf64_Ehdr); shdr_size = sizeof(Elf64_Shdr); } #undef LOAD_HEADER @@ -330,8 +329,9 @@ struct kmod_elf *kmod_elf_new(const void *memory, off_t size) elf->header.section.entry_size, shdr_size); goto invalid; } - min_size = hdr_size + shdr_size * elf->header.section.count; - if (min_size >= elf->size) { + shdrs_size = shdr_size * elf->header.section.count; + if (addu64_overflow(shdrs_size, elf->header.section.offset, &min_size) + || min_size > elf->size) { ELFDBG(elf, "file is too short to hold sections\n"); goto invalid; } |