Validate properties of the strtab that are depended on elsewhere, but were previously unchecked: * String table nonempty (offset 0 is valid) * String table has a leading NUL (offset 0 corresponds to "") * String table is NUL terminated (strfoo functions won't run out of the table while reading). * All symbols names are inbounds of the string table.
Signed-off-by: Matthew Maurer <mmau...@google.com> --- kernel/module/main.c | 38 +++++++++++++++++++++++++++++++++++++- 1 file changed, 37 insertions(+), 1 deletion(-) diff --git a/kernel/module/main.c b/kernel/module/main.c index c082d5d41a8d..b40b632f00a6 100644 --- a/kernel/module/main.c +++ b/kernel/module/main.c @@ -2090,17 +2090,53 @@ static int elf_validity_cache_index(struct load_info *info, int flags) } /** - * elf_validity_cache_strtab() - Cache symbol string table + * elf_validity_cache_strtab() - Validate and cache symbol string table * @info: Load info to read from and update. * Must have &load_info->sechdrs and &load_info->secstrings populated. * Must have &load_info->index populated. * + * Checks: + * + * * The string table is not empty. + * * The string table starts and ends with NUL (required by ELF spec). + * * Every &Elf_Sym->st_name offset in the symbol table is inbounds of the + * string table. + * + * And caches the pointer as &load_info->strtab in @info. + * * Return: 0 on success, negative error code if a check failed. */ static int elf_validity_cache_strtab(struct load_info *info) { Elf_Shdr *str_shdr = &info->sechdrs[info->index.str]; + Elf_Shdr *sym_shdr = &info->sechdrs[info->index.sym]; char *strtab = (char *)info->hdr + str_shdr->sh_offset; + Elf_Sym *syms = (void *)info->hdr + sym_shdr->sh_offset; + int i; + + if (str_shdr->sh_size == 0) { + pr_err("empty symbol string table\n"); + return -ENOEXEC; + } + if (strtab[0] != '\0') { + pr_err("symbol string table missing leading NUL\n"); + return -ENOEXEC; + } + if (strtab[str_shdr->sh_size - 1] != '\0') { + pr_err("symbol string table isn't NUL terminated\n"); + return -ENOEXEC; + } + + /* + * Now that we know strtab is correctly structured, check symbol + * starts are inbounds before they're used later. + */ + for (i = 0; i < sym_shdr->sh_size / sizeof(*syms); i++) { + if (syms[i].st_name >= str_shdr->sh_size) { + pr_err("symbol name out of bounds in string table"); + return -ENOEXEC; + } + } info->strtab = strtab; return 0; -- 2.46.1.824.gd892dcdcdd-goog