From: Alexey Dobriyan <adobriyan@gmail.com>
Date: Wed, 4 May 2022 12:54:20 +0300
Subject: module: fix [e_shstrndx].sh_size=0 OOB access
Git-commit: 391e982bfa632b8315235d8be9c0a81374c6a19c
Patch-mainline: v5.19-rc1
References: git-fixes

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
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>
[rebased patch onto modules-next]
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
[ppavlu: s,kernel/module/main.c,kernel/module.c, because we don't have
 commit cfc1d277891e ("module: Move all into module/").]
Acked-by: Petr Pavlu <petr.pavlu@suse.com>
---
 kernel/module.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/module.c b/kernel/module.c
index 6c3b4a846645..23432fabfde8 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -1726,6 +1726,10 @@ 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;