linux-kernel - [PATCH 1/3] sysctl: Fix out of bounds access for empty sysctl registers

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Message-Id: <20231121-jag-fix_out_of_bounds_insert-v1-1-571e76d51316@samsung.com>
Date:   Tue, 21 Nov 2023 12:02:18 +0100
From:   Joel Granados via B4 Relay 
        <devnull+j.granados.samsung.com@...nel.org>
To:     Luis Chamberlain <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Iurii Zaikin <yzaikin@...gle.com>,
        Shuah Khan <shuah@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kselftest@...r.kernel.org,
        Joel Granados <j.granados@...sung.com>,
        kernel test robot <oliver.sang@...el.com>
Subject: [PATCH 1/3] sysctl: Fix out of bounds access for empty sysctl
 registers

From: Joel Granados <j.granados@...sung.com>

When registering tables to the sysctl subsystem there is a check to see
if header is a permanently empty directory (used for mounts). This check
evaluates the first element of the ctl_table. This results in an out of
bounds evaluation when registering empty directories.

The function register_sysctl_mount_point now passes a ctl_table of size
1 instead of size 0. It now relies solely on the type to identify
a permanently empty register.

Make sure that the ctl_table has at least one element before testing for
permanent emptiness.

Signed-off-by: Joel Granados <j.granados@...sung.com>
Reported-by: kernel test robot <oliver.sang@...el.com>
Closes: https://lore.kernel.org/oe-lkp/202311201431.57aae8f3-oliver.sang@intel.com
---
 fs/proc/proc_sysctl.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
index de484195f49f..5b5cdc747cef 100644
--- a/fs/proc/proc_sysctl.c
+++ b/fs/proc/proc_sysctl.c
@@ -44,7 +44,7 @@ static struct ctl_table sysctl_mount_point[] = {
  */
 struct ctl_table_header *register_sysctl_mount_point(const char *path)
 {
-	return register_sysctl_sz(path, sysctl_mount_point, 0);
+	return register_sysctl(path, sysctl_mount_point);
 }
 EXPORT_SYMBOL(register_sysctl_mount_point);
 
@@ -233,7 +233,8 @@ static int insert_header(struct ctl_dir *dir, struct ctl_table_header *header)
 		return -EROFS;
 
 	/* Am I creating a permanently empty directory? */
-	if (sysctl_is_perm_empty_ctl_table(header->ctl_table)) {
+	if (header->ctl_table_size > 0 &&
+	    sysctl_is_perm_empty_ctl_table(header->ctl_table)) {
 		if (!RB_EMPTY_ROOT(&dir->root))
 			return -EINVAL;
 		sysctl_set_perm_empty_ctl_header(dir_h);
@@ -1213,6 +1214,10 @@ static bool get_links(struct ctl_dir *dir,
 	struct ctl_table_header *tmp_head;
 	struct ctl_table *entry, *link;
 
+	if (header->ctl_table_size == 0 ||
+	    sysctl_is_perm_empty_ctl_table(header->ctl_table))
+		return true;
+
 	/* Are there links available for every entry in table? */
 	list_for_each_table_entry(entry, header) {
 		const char *procname = entry->procname;

-- 
2.30.2