1 files changed, 156 insertions, 31 deletions

diff --git a/kernel/module.c b/kernel/module.c
index 9e9af40698ff..c60559b5bf10 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2310,6 +2310,21 @@ static int verify_exported_symbols(struct module *mod)
 	return 0;
 }
 
+static bool ignore_undef_symbol(Elf_Half emachine, const char *name)
+{
+	/*
+	 * On x86, PIC code and Clang non-PIC code may have call foo@PLT. GNU as
+	 * before 2.37 produces an unreferenced _GLOBAL_OFFSET_TABLE_ on x86-64.
+	 * i386 has a similar problem but may not deserve a fix.
+	 *
+	 * If we ever have to ignore many symbols, consider refactoring the code to
+	 * only warn if referenced by a relocation.
+	 */
+	if (emachine == EM_386 || emachine == EM_X86_64)
+		return !strcmp(name, "_GLOBAL_OFFSET_TABLE_");
+	return false;
+}
+
 /* Change all symbols so that st_value encodes the pointer directly. */
 static int simplify_symbols(struct module *mod, const struct load_info *info)
 {
@@ -2355,8 +2370,10 @@ static int simplify_symbols(struct module *mod, const struct load_info *info)
 				break;
 			}
 
-			/* Ok if weak.  */
-			if (!ksym && ELF_ST_BIND(sym[i].st_info) == STB_WEAK)
+			/* Ok if weak or ignored.  */
+			if (!ksym &&
+			    (ELF_ST_BIND(sym[i].st_info) == STB_WEAK ||
+			     ignore_undef_symbol(info->hdr->e_machine, name)))
 				break;
 
 			ret = PTR_ERR(ksym) ?: -ENOENT;
@@ -2891,20 +2908,14 @@ static int module_sig_check(struct load_info *info, int flags)
 		 * enforcing, certain errors are non-fatal.
 		 */
 	case -ENODATA:
-		reason = "Loading of unsigned module";
-		goto decide;
+		reason = "unsigned module";
+		break;
 	case -ENOPKG:
-		reason = "Loading of module with unsupported crypto";
-		goto decide;
+		reason = "module with unsupported crypto";
+		break;
 	case -ENOKEY:
-		reason = "Loading of module with unavailable key";
-	decide:
-		if (is_module_sig_enforced()) {
-			pr_notice("%s is rejected\n", reason);
-			return -EKEYREJECTED;
-		}
-
-		return security_locked_down(LOCKDOWN_MODULE_SIGNATURE);
+		reason = "module with unavailable key";
+		break;
 
 		/* All other errors are fatal, including nomem, unparseable
 		 * signatures and signature check failures - even if signatures
@@ -2913,6 +2924,13 @@ static int module_sig_check(struct load_info *info, int flags)
 	default:
 		return err;
 	}
+
+	if (is_module_sig_enforced()) {
+		pr_notice("Loading of %s is rejected\n", reason);
+		return -EKEYREJECTED;
+	}
+
+	return security_locked_down(LOCKDOWN_MODULE_SIGNATURE);
 }
 #else /* !CONFIG_MODULE_SIG */
 static int module_sig_check(struct load_info *info, int flags)
@@ -2921,9 +2939,33 @@ static int module_sig_check(struct load_info *info, int flags)
 }
 #endif /* !CONFIG_MODULE_SIG */
 
-/* Sanity checks against invalid binaries, wrong arch, weird elf version. */
-static int elf_header_check(struct load_info *info)
+static int validate_section_offset(struct load_info *info, Elf_Shdr *shdr)
 {
+	unsigned long secend;
+
+	/*
+	 * Check for both overflow and offset/size being
+	 * too large.
+	 */
+	secend = shdr->sh_offset + shdr->sh_size;
+	if (secend < shdr->sh_offset || secend > info->len)
+		return -ENOEXEC;
+
+	return 0;
+}
+
+/*
+ * Sanity checks against invalid binaries, wrong arch, weird elf version.
+ *
+ * Also do basic validity checks against section offsets and sizes, the
+ * section name string table, and the indices used for it (sh_name).
+ */
+static int elf_validity_check(struct load_info *info)
+{
+	unsigned int i;
+	Elf_Shdr *shdr, *strhdr;
+	int err;
+
 	if (info->len < sizeof(*(info->hdr)))
 		return -ENOEXEC;
 
@@ -2933,11 +2975,78 @@ static int elf_header_check(struct load_info *info)
 	    || info->hdr->e_shentsize != sizeof(Elf_Shdr))
 		return -ENOEXEC;
 
+	/*
+	 * e_shnum is 16 bits, and sizeof(Elf_Shdr) is
+	 * known and small. So e_shnum * sizeof(Elf_Shdr)
+	 * will not overflow unsigned long on any platform.
+	 */
 	if (info->hdr->e_shoff >= info->len
 	    || (info->hdr->e_shnum * sizeof(Elf_Shdr) >
 		info->len - info->hdr->e_shoff))
 		return -ENOEXEC;
 
+	info->sechdrs = (void *)info->hdr + info->hdr->e_shoff;
+
+	/*
+	 * Verify if the section name table index is valid.
+	 */
+	if (info->hdr->e_shstrndx == SHN_UNDEF
+	    || info->hdr->e_shstrndx >= info->hdr->e_shnum)
+		return -ENOEXEC;
+
+	strhdr = &info->sechdrs[info->hdr->e_shstrndx];
+	err = validate_section_offset(info, strhdr);
+	if (err < 0)
+		return err;
+
+	/*
+	 * The section name table must be NUL-terminated, as required
+	 * by the spec. This makes strcmp and pr_* calls that access
+	 * strings in the section safe.
+	 */
+	info->secstrings = (void *)info->hdr + strhdr->sh_offset;
+	if (info->secstrings[strhdr->sh_size - 1] != '\0')
+		return -ENOEXEC;
+
+	/*
+	 * The code assumes that section 0 has a length of zero and
+	 * an addr of zero, so check for it.
+	 */
+	if (info->sechdrs[0].sh_type != SHT_NULL
+	    || info->sechdrs[0].sh_size != 0
+	    || info->sechdrs[0].sh_addr != 0)
+		return -ENOEXEC;
+
+	for (i = 1; i < info->hdr->e_shnum; i++) {
+		shdr = &info->sechdrs[i];
+		switch (shdr->sh_type) {
+		case SHT_NULL:
+		case SHT_NOBITS:
+			continue;
+		case SHT_SYMTAB:
+			if (shdr->sh_link == SHN_UNDEF
+			    || shdr->sh_link >= info->hdr->e_shnum)
+				return -ENOEXEC;
+			fallthrough;
+		default:
+			err = validate_section_offset(info, shdr);
+			if (err < 0) {
+				pr_err("Invalid ELF section in module (section %u type %u)\n",
+					i, shdr->sh_type);
+				return err;
+			}
+
+			if (shdr->sh_flags & SHF_ALLOC) {
+				if (shdr->sh_name >= strhdr->sh_size) {
+					pr_err("Invalid ELF section name in module (section %u type %u)\n",
+					       i, shdr->sh_type);
+					return -ENOEXEC;
+				}
+			}
+			break;
+		}
+	}
+
 	return 0;
 }
 
@@ -3034,11 +3143,6 @@ static int rewrite_section_headers(struct load_info *info, int flags)
 
 	for (i = 1; i < info->hdr->e_shnum; i++) {
 		Elf_Shdr *shdr = &info->sechdrs[i];
-		if (shdr->sh_type != SHT_NOBITS
-		    && info->len < shdr->sh_offset + shdr->sh_size) {
-			pr_err("Module len %lu truncated\n", info->len);
-			return -ENOEXEC;
-		}
 
 		/* Mark all sections sh_addr with their address in the
 		   temporary image. */
@@ -3070,11 +3174,6 @@ static int setup_load_info(struct load_info *info, int flags)
 {
 	unsigned int i;
 
-	/* Set up the convenience variables */
-	info->sechdrs = (void *)info->hdr + info->hdr->e_shoff;
-	info->secstrings = (void *)info->hdr
-		+ info->sechdrs[info->hdr->e_shstrndx].sh_offset;
-
 	/* Try to find a name early so we can log errors with a module name */
 	info->index.info = find_sec(info, ".modinfo");
 	if (info->index.info)
@@ -3802,23 +3901,49 @@ static int load_module(struct load_info *info, const char __user *uargs,
 	long err = 0;
 	char *after_dashes;
 
-	err = elf_header_check(info);
+	/*
+	 * Do the signature check (if any) first. All that
+	 * the signature check needs is info->len, it does
+	 * not need any of the section info. That can be
+	 * set up later. This will minimize the chances
+	 * of a corrupt module causing problems before
+	 * we even get to the signature check.
+	 *
+	 * The check will also adjust info->len by stripping
+	 * off the sig length at the end of the module, making
+	 * checks against info->len more correct.
+	 */
+	err = module_sig_check(info, flags);
 	if (err)
 		goto free_copy;
 
+	/*
+	 * Do basic sanity checks against the ELF header and
+	 * sections.
+	 */
+	err = elf_validity_check(info);
+	if (err) {
+		pr_err("Module has invalid ELF structures\n");
+		goto free_copy;
+	}
+
+	/*
+	 * Everything checks out, so set up the section info
+	 * in the info structure.
+	 */
 	err = setup_load_info(info, flags);
 	if (err)
 		goto free_copy;
 
+	/*
+	 * Now that we know we have the correct module name, check
+	 * if it's blacklisted.
+	 */
 	if (blacklisted(info->name)) {
 		err = -EPERM;
 		goto free_copy;
 	}
 
-	err = module_sig_check(info, flags);
-	if (err)
-		goto free_copy;
-
 	err = rewrite_section_headers(info, flags);
 	if (err)
 		goto free_copy;