Re: [PATCH 1/3] ext4: avoid potential buffer over-read in parse_apply_sb_mount_options()
From: "Darrick J. Wong" <djwong@kernel.org>
Date: 2025-09-11 22:27:01
Also in:
linux-ext4, stable
On Mon, Sep 08, 2025 at 11:15:48PM -0400, Theodore Ts'o via B4 Relay wrote:
From: Theodore Ts'o <tytso@mit.edu> Unlike other strings in the ext4 superblock, we rely on tune2fs to make sure s_mount_opts is NUL terminated. Harden parse_apply_sb_mount_options() by treating s_mount_opts as a potential __nonstring.
Uh.... does that mean that a filesystem with exactly 64 bytes worth of mount option string (and no trailing null) could do something malicious? My guess is that s_usr_quota_inum mostly saves us, but a nastycrafted filesystem with more than 2^24 inodes could cause an out of bounds memory access? But that most likely will just fail the mount option parser anyway? --D
quoted hunk ↗ jump to hunk
Cc: stable@vger.kernel.org Fixes: 8b67f04ab9de ("ext4: Add mount options in superblock") Signed-off-by: Theodore Ts'o <tytso@mit.edu> --- fs/ext4/super.c | 17 +++++------------ 1 file changed, 5 insertions(+), 12 deletions(-)diff --git a/fs/ext4/super.c b/fs/ext4/super.c index 699c15db28a82f26809bf68533454a242596f0fd..94c98446c84f9a4614971d246ca7f001de610a8a 100644 --- a/fs/ext4/super.c +++ b/fs/ext4/super.c@@ -2460,7 +2460,7 @@ static int parse_apply_sb_mount_options(struct super_block *sb, struct ext4_fs_context *m_ctx) { struct ext4_sb_info *sbi = EXT4_SB(sb); - char *s_mount_opts = NULL; + char s_mount_opts[65]; struct ext4_fs_context *s_ctx = NULL; struct fs_context *fc = NULL; int ret = -ENOMEM;@@ -2468,15 +2468,11 @@ static int parse_apply_sb_mount_options(struct super_block *sb, if (!sbi->s_es->s_mount_opts[0]) return 0; - s_mount_opts = kstrndup(sbi->s_es->s_mount_opts, - sizeof(sbi->s_es->s_mount_opts), - GFP_KERNEL); - if (!s_mount_opts) - return ret; + strscpy_pad(s_mount_opts, sbi->s_es->s_mount_opts); fc = kzalloc(sizeof(struct fs_context), GFP_KERNEL); if (!fc) - goto out_free; + return -ENOMEM; s_ctx = kzalloc(sizeof(struct ext4_fs_context), GFP_KERNEL); if (!s_ctx)@@ -2508,11 +2504,8 @@ static int parse_apply_sb_mount_options(struct super_block *sb, ret = 0; out_free: - if (fc) { - ext4_fc_free(fc); - kfree(fc); - } - kfree(s_mount_opts); + ext4_fc_free(fc); + kfree(fc); return ret; }-- 2.51.0