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Date:   Wed, 4 May 2022 12:54:20 +0300
From:   Alexey Dobriyan <adobriyan@gmail.com>
To:     Luis Chamberlain <mcgrof@kernel.org>
Cc:     akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
        linux-modules@vger.kernel.org,
        Frank van der Linden <fllinden@amazon.com>
Subject: [PATCH v2] module: fix [e_shstrndx].sh_size=0 OOB access
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References: <YnFC93NVRqOterbV@localhost.localdomain>
 <YnGNSNcUbkwLNWNd@bombadil.infradead.org>
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It is trivial to craft a module to trigger OOB access in this line:

	if (info->secstrings[strhdr->sh_size - 1] != '\0') {

BUG: unable to handle page fault for address: ffffc90000aa0fff
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 100000067 P4D 100000067 PUD 100066067 PMD 10436f067 PTE 0
Oops: 0000 [#1] PREEMPT SMP PTI
CPU: 7 PID: 1215 Comm: insmod Not tainted 5.18.0-rc5-00007-g9bf578647087-dirty #10
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-4.fc34 04/01/2014
RIP: 0010:load_module+0x19b/0x2391

Fixes: ec2a29593c83 ("module: harden ELF info handling")
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
---

 kernel/module.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/kernel/module.c
+++ b/kernel/module.c
@@ -3033,6 +3033,10 @@ static int elf_validity_check(struct load_info *info)
 	 * strings in the section safe.
 	 */
 	info->secstrings = (void *)info->hdr + strhdr->sh_offset;
+	if (strhdr->sh_size == 0) {
+		pr_err("empty section name table\n");
+		goto no_exec;
+	}
 	if (info->secstrings[strhdr->sh_size - 1] != '\0') {
 		pr_err("ELF Spec violation: section name table isn't null terminated\n");
 		goto no_exec;


Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
---

 kernel/module.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/kernel/module.c
+++ b/kernel/module.c
@@ -3033,6 +3033,10 @@ static int elf_validity_check(struct load_info *info)
 	 * strings in the section safe.
 	 */
 	info->secstrings = (void *)info->hdr + strhdr->sh_offset;
+	if (strhdr->sh_size == 0) {
+		pr_err("empty section name table\n");
+		goto no_exec;
+	}
 	if (info->secstrings[strhdr->sh_size - 1] != '\0') {
 		pr_err("ELF Spec violation: section name table isn't null terminated\n");
 		goto no_exec;