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AJvYcCWxfjliaoNtdHT8QdXzl04zlAgIJcvC5T4giU+SL4kSvc7xMhBs7Ow3ye3I0+ffl0zTCvfH6LObWAvi4eeVPX2WaQTcuU4yx/tcb0mh X-Gm-Message-State: AOJu0Yxyu9AwF/UvAliJVFYXWZL6AxA6Lsp0WzyW14QPgisP2kcPeQ+W f2OwnNFVVoVAEpPZV+P56MYzQVpOsJasRbnn/S+AGAnKSYt9SGmIP4kU1FTNqTU/KzXXdMPNMiB 3RTukag== X-Google-Smtp-Source: AGHT+IH6x1pd7T7CSwv3R+eylAyRZmNxI/232pEEFyoDFtMxFDuEMBONgvXpuP7EkLOuGdtv0x2gUeU1cK01 X-Received: from anyblade.c.googlers.com ([fda3:e722:ac3:cc00:20:ed76:c0a8:1791]) (user=mmaurer job=sendgmr) by 2002:a05:6902:100c:b0:dfa:8ed1:8f1b with SMTP id 3f1490d57ef6-e0bde22affamr345027276.1.1722979292488; Tue, 06 Aug 2024 14:21:32 -0700 (PDT) Date: Tue, 6 Aug 2024 21:20:37 +0000 In-Reply-To: <20240806212106.617164-1-mmaurer@google.com> Precedence: bulk X-Mailing-List: linux-kbuild@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20240806212106.617164-1-mmaurer@google.com> X-Mailer: git-send-email 2.46.0.rc2.264.g509ed76dc8-goog Message-ID: <20240806212106.617164-12-mmaurer@google.com> Subject: [PATCH v3 11/16] module: Additional validation in elf_validity_cache_strtab From: Matthew Maurer To: masahiroy@kernel.org, ndesaulniers@google.com, ojeda@kernel.org, gary@garyguo.net, mcgrof@kernel.org, Alex Gaynor , Wedson Almeida Filho Cc: Matthew Maurer , rust-for-linux@vger.kernel.org, linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, neal@gompa.dev, marcan@marcan.st, j@jannau.net, asahi@lists.linux.dev, Boqun Feng , " =?utf-8?q?Bj=C3=B6rn_Roy_Baron?= " , Benno Lossin , Andreas Hindborg , Alice Ryhl , linux-modules@vger.kernel.org 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 --- 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 d70d829b5ab9..7001054c5c4f 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;