From 2d58bf6a037c8ad474db4a902e799bee637e7ec0 Mon Sep 17 00:00:00 2001 From: Jacob Garber Date: Tue, 2 Jul 2019 14:38:38 -0600 Subject: util/cbfstool: Prevent overflow of 16 bit multiplications Considering the following integer multiplication: u64 = u16 * u16 What on earth, one might wonder, is the problem with this? Well, due to C's unfortunately abstruse integer semantics, both u16's are implicitly converted to int before the multiplication, which cannot hold all possible values of a u16 * u16. Even worse, after overflow the intermediate result will be a negative number, which during the conversion to a u64 will be sign-extended to a huge integer. Not good. The solution is to manually cast one of the u16 to a u32 or u64, which are large enough to not have any overflow and will prevent the implicit conversion. The type of the u64 is preferred, though a u32 is used instead of size_t, since that can change depending on the platform. Change-Id: I5391221d46d620d0e5bd629e2f9680be7a53342e Signed-off-by: Jacob Garber Found-by: Coverity CID 12297{03,04,05,06,07,08,09,10} Reviewed-on: https://review.coreboot.org/c/coreboot/+/33986 Tested-by: build bot (Jenkins) Reviewed-by: Julius Werner Reviewed-by: Paul Menzel --- util/cbfstool/elfheaders.c | 14 ++++++++------ 1 file changed, 8 insertions(+), 6 deletions(-) (limited to 'util/cbfstool') diff --git a/util/cbfstool/elfheaders.c b/util/cbfstool/elfheaders.c index 8da54d09e0..676a635b8a 100644 --- a/util/cbfstool/elfheaders.c +++ b/util/cbfstool/elfheaders.c @@ -262,7 +262,8 @@ phdr_read(const struct buffer *in, struct parsed_elf *pelf, * per the ELF spec, You'd be surprised how many ELF * readers miss this little detail. */ - buffer_splice(&b, in, ehdr->e_phoff, ehdr->e_phentsize * ehdr->e_phnum); + buffer_splice(&b, in, ehdr->e_phoff, + (uint32_t)ehdr->e_phentsize * ehdr->e_phnum); if (check_size(in, ehdr->e_phoff, buffer_size(&b), "program headers")) return -1; @@ -304,7 +305,8 @@ shdr_read(const struct buffer *in, struct parsed_elf *pelf, * per the ELF spec, You'd be surprised how many ELF * readers miss this little detail. */ - buffer_splice(&b, in, ehdr->e_shoff, ehdr->e_shentsize * ehdr->e_shnum); + buffer_splice(&b, in, ehdr->e_shoff, + (uint32_t)ehdr->e_shentsize * ehdr->e_shnum); if (check_size(in, ehdr->e_shoff, buffer_size(&b), "section headers")) return -1; @@ -1180,8 +1182,8 @@ int elf_writer_serialize(struct elf_writer *ew, struct buffer *out) ew->ehdr.e_shnum = ew->num_secs; metadata_size = 0; metadata_size += ew->ehdr.e_ehsize; - metadata_size += ew->ehdr.e_shnum * ew->ehdr.e_shentsize; - metadata_size += ew->ehdr.e_phnum * ew->ehdr.e_phentsize; + metadata_size += (Elf64_Xword)ew->ehdr.e_shnum * ew->ehdr.e_shentsize; + metadata_size += (Elf64_Xword)ew->ehdr.e_phnum * ew->ehdr.e_phentsize; shstroffset = metadata_size; /* Align up section header string size and metadata size to 4KiB */ metadata_size = ALIGN(metadata_size + shstrlen, 4096); @@ -1200,11 +1202,11 @@ int elf_writer_serialize(struct elf_writer *ew, struct buffer *out) */ ew->ehdr.e_shoff = ew->ehdr.e_ehsize; ew->ehdr.e_phoff = ew->ehdr.e_shoff + - ew->ehdr.e_shnum * ew->ehdr.e_shentsize; + (Elf64_Off)ew->ehdr.e_shnum * ew->ehdr.e_shentsize; buffer_splice(&metadata, out, 0, metadata_size); buffer_splice(&phdrs, out, ew->ehdr.e_phoff, - ew->ehdr.e_phnum * ew->ehdr.e_phentsize); + (uint32_t)ew->ehdr.e_phnum * ew->ehdr.e_phentsize); buffer_splice(&data, out, metadata_size, program_size); /* Set up the section header string table contents. */ strtab = &ew->shstrtab_sec->content; -- cgit v1.2.3