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AJvYcCU4Y6ucBjibJAMYraq8EPc25+KFghn3ZCL7K2t/TGv7bxHuaeTvSSV7iQgAulnNhXvJ8wnAtA==@lists.linux.dev X-Gm-Message-State: AOJu0YwLVgAIfxWsKg1a97aNKyoWnTGxCbdbw4c96hVX930Z64yC7rNz HlCLFO3CH1IFTRTh0Ha+fccm7v+2VhjSy45lbD8dW2FxdcZIKcr2tyyx1KvB+47H+CnpK7RS40W MQaQAJQ== X-Google-Smtp-Source: AGHT+IFOctLtu2fDpWSwtgdrlWQhzeyg6ur9X7N6yKJb4yvjNshlLawCmOC09mIbp13RxLe82I6Qn8MDC9MI X-Received: from anyblade.c.googlers.com ([fda3:e722:ac3:cc00:20:ed76:c0a8:1791]) (user=mmaurer job=sendgmr) by 2002:a05:690c:6583:b0:6dd:bc47:1ce1 with SMTP id 00721157ae682-6e21d0b47e5mr368107b3.0.1727307586448; Wed, 25 Sep 2024 16:39:46 -0700 (PDT) Date: Wed, 25 Sep 2024 23:38:26 +0000 In-Reply-To: <20240925233854.90072-1-mmaurer@google.com> Precedence: bulk X-Mailing-List: asahi@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20240925233854.90072-1-mmaurer@google.com> X-Mailer: git-send-email 2.46.1.824.gd892dcdcdd-goog Message-ID: <20240925233854.90072-12-mmaurer@google.com> Subject: [PATCH v5 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 Cc: 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, linux-modules@vger.kernel.org, Matthew Maurer , Petr Pavlu , Sami Tolvanen , Daniel Gomez , Boqun Feng , "=?UTF-8?q?Bj=C3=B6rn=20Roy=20Baron?=" , Benno Lossin , Andreas Hindborg , Alice Ryhl , Trevor Gross Content-Type: text/plain; charset="UTF-8" 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 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