[PATCH 4.9 17/97] ext4: fix use-after-free race with debug_want_extra_isize

Greg Kroah-Hartman
2020-01-22T09:35:26Z

From: Barret Rhoden <brho@google.com>

commit 7bc04c5c2cc467c5b40f2b03ba08da174a0d5fa7 upstream.

When remounting with debug_want_extra_isize, we were not performing the
same checks that we do during a normal mount. That allowed us to set a
value for s_want_extra_isize that reached outside the s_inode_size.

Fixes: e2b911c53584 ("ext4: clean up feature test macros with predicate functions")
Reported-by: syzbot+f584efa0ac7213c226b7@syzkaller.appspotmail.com
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Barret Rhoden <brho@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
[bwh: Backported to 4.9: The debug_want_extra_isize mount option is not
supported]
Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/ext4/super.c | 56 +++++++++++++++++++++++++++++++++-----------------------
1 file changed, 33 insertions(+), 23 deletions(-)

--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3342,6 +3342,36 @@ int ext4_calculate_overhead(struct super
return 0;
}

+static void ext4_clamp_want_extra_isize(struct super_block *sb)
+{
+ struct ext4_sb_info *sbi = EXT4_SB(sb);
+ struct ext4_super_block *es = sbi->s_es;
+
+ /* determine the minimum size of new large inodes, if present */
+ if (sbi->s_inode_size > EXT4_GOOD_OLD_INODE_SIZE) {
+ sbi->s_want_extra_isize = sizeof(struct ext4_inode) -
+ EXT4_GOOD_OLD_INODE_SIZE;
+ if (ext4_has_feature_extra_isize(sb)) {
+ if (sbi->s_want_extra_isize <
+ le16_to_cpu(es->s_want_extra_isize))
+ sbi->s_want_extra_isize =
+ le16_to_cpu(es->s_want_extra_isize);
+ if (sbi->s_want_extra_isize <
+ le16_to_cpu(es->s_min_extra_isize))
+ sbi->s_want_extra_isize =
+ le16_to_cpu(es->s_min_extra_isize);
+ }
+ }
+ /* Check if enough inode space is available */
+ if (EXT4_GOOD_OLD_INODE_SIZE + sbi->s_want_extra_isize >
+ sbi->s_inode_size) {
+ sbi->s_want_extra_isize = sizeof(struct ext4_inode) -
+ EXT4_GOOD_OLD_INODE_SIZE;
+ ext4_msg(sb, KERN_INFO,
+ "required extra inode space not available");
+ }
+}
+
static void ext4_set_resv_clusters(struct super_block *sb)
{
ext4_fsblk_t resv_clusters;
@@ -4156,29 +4186,7 @@ no_journal:
if (ext4_setup_super(sb, es, sb->s_flags & MS_RDONLY))
sb->s_flags |= MS_RDONLY;

- /* determine the minimum size of new large inodes, if present */
- if (sbi->s_inode_size > EXT4_GOOD_OLD_INODE_SIZE) {
- sbi->s_want_extra_isize = sizeof(struct ext4_inode) -
- EXT4_GOOD_OLD_INODE_SIZE;
- if (ext4_has_feature_extra_isize(sb)) {
- if (sbi->s_want_extra_isize <
- le16_to_cpu(es->s_want_extra_isize))
- sbi->s_want_extra_isize =
- le16_to_cpu(es->s_want_extra_isize);
- if (sbi->s_want_extra_isize <
- le16_to_cpu(es->s_min_extra_isize))
- sbi->s_want_extra_isize =
- le16_to_cpu(es->s_min_extra_isize);
- }
- }
- /* Check if enough inode space is available */
- if (EXT4_GOOD_OLD_INODE_SIZE + sbi->s_want_extra_isize >
- sbi->s_inode_size) {
- sbi->s_want_extra_isize = sizeof(struct ext4_inode) -
- EXT4_GOOD_OLD_INODE_SIZE;
- ext4_msg(sb, KERN_INFO, "required extra inode space not"
- "available");
- }
+ ext4_clamp_want_extra_isize(sb);

ext4_set_resv_clusters(sb);

@@ -4959,6 +4967,8 @@ static int ext4_remount(struct super_blo
goto restore_opts;
}

+ ext4_clamp_want_extra_isize(sb);
+
if ((old_opts.s_mount_opt & EXT4_MOUNT_JOURNAL_CHECKSUM) ^
test_opt(sb, JOURNAL_CHECKSUM)) {
ext4_msg(sb, KERN_ERR, "changing journal_checksum "