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SubjectRe: KASAN: use-after-free Read in ext4_xattr_set_entry (2)
On Sat, Dec 14, 2019 at 05:27:00PM -0800, syzbot wrote:
> syzbot has bisected this bug to:
>
> commit 8835cae5f2abd7f7a3143afe357f416aff5517a4
> Author: Chris Lapa <chris@lapa.com.au>
> Date: Wed Jan 11 01:44:47 2017 +0000
>
> power: supply: bq27xxx: adds specific support for bq27520-g4 revision.

This is pretty clearly nonsense. However let's try this fix:

#syz test: https://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4.git master

From 9c962de70a52e0b24fba00ee7b8707964d3d1e37 Mon Sep 17 00:00:00 2001
From: Theodore Ts'o <tytso@mit.edu>
Date: Sun, 15 Dec 2019 01:09:03 -0500
Subject: [PATCH] ext4: validate the debug_want_extra_isize mount option at parse time

Instead of setting s_want_extra_size and then making sure that it is a
valid value afterwards, validate the field before we set it. This
avoids races and other problems when remounting the file system.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reported-by: syzbot+4a39a025912b265cacef@syzkaller.appspotmail.com
---
fs/ext4/super.c | 143 +++++++++++++++++++++++-------------------------
1 file changed, 69 insertions(+), 74 deletions(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index b205112ca051..46b6d5b150ac 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -1886,6 +1886,13 @@ static int handle_mount_opt(struct super_block *sb, char *opt, int token,
}
sbi->s_commit_interval = HZ * arg;
} else if (token == Opt_debug_want_extra_isize) {
+ if ((arg & 1) ||
+ (arg < 4) ||
+ (arg > (sbi->s_inode_size - EXT4_GOOD_OLD_INODE_SIZE))) {
+ ext4_msg(sb, KERN_ERR,
+ "Invalid want_extra_isize %d", arg);
+ return -1;
+ }
sbi->s_want_extra_isize = arg;
} else if (token == Opt_max_batch_time) {
sbi->s_max_batch_time = arg;
@@ -3540,40 +3547,6 @@ int ext4_calculate_overhead(struct super_block *sb)
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;
- unsigned def_extra_isize = sizeof(struct ext4_inode) -
- EXT4_GOOD_OLD_INODE_SIZE;
-
- if (sbi->s_inode_size == EXT4_GOOD_OLD_INODE_SIZE) {
- sbi->s_want_extra_isize = 0;
- return;
- }
- if (sbi->s_want_extra_isize < 4) {
- sbi->s_want_extra_isize = def_extra_isize;
- 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 ((sbi->s_want_extra_isize > sbi->s_inode_size) ||
- (EXT4_GOOD_OLD_INODE_SIZE + sbi->s_want_extra_isize >
- sbi->s_inode_size)) {
- sbi->s_want_extra_isize = def_extra_isize;
- 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;
@@ -3781,6 +3754,68 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
*/
sbi->s_li_wait_mult = EXT4_DEF_LI_WAIT_MULT;

+ if (le32_to_cpu(es->s_rev_level) == EXT4_GOOD_OLD_REV) {
+ sbi->s_inode_size = EXT4_GOOD_OLD_INODE_SIZE;
+ sbi->s_first_ino = EXT4_GOOD_OLD_FIRST_INO;
+ } else {
+ sbi->s_inode_size = le16_to_cpu(es->s_inode_size);
+ sbi->s_first_ino = le32_to_cpu(es->s_first_ino);
+ if (sbi->s_first_ino < EXT4_GOOD_OLD_FIRST_INO) {
+ ext4_msg(sb, KERN_ERR, "invalid first ino: %u",
+ sbi->s_first_ino);
+ goto failed_mount;
+ }
+ if ((sbi->s_inode_size < EXT4_GOOD_OLD_INODE_SIZE) ||
+ (!is_power_of_2(sbi->s_inode_size)) ||
+ (sbi->s_inode_size > blocksize)) {
+ ext4_msg(sb, KERN_ERR,
+ "unsupported inode size: %d",
+ sbi->s_inode_size);
+ goto failed_mount;
+ }
+ /*
+ * i_atime_extra is the last extra field available for
+ * [acm]times in struct ext4_inode. Checking for that
+ * field should suffice to ensure we have extra space
+ * for all three.
+ */
+ if (sbi->s_inode_size >= offsetof(struct ext4_inode, i_atime_extra) +
+ sizeof(((struct ext4_inode *)0)->i_atime_extra)) {
+ sb->s_time_gran = 1;
+ sb->s_time_max = EXT4_EXTRA_TIMESTAMP_MAX;
+ } else {
+ sb->s_time_gran = NSEC_PER_SEC;
+ sb->s_time_max = EXT4_NON_EXTRA_TIMESTAMP_MAX;
+ }
+ sb->s_time_min = EXT4_TIMESTAMP_MIN;
+ }
+ 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)) {
+ unsigned v, max = (sbi->s_inode_size -
+ EXT4_GOOD_OLD_INODE_SIZE);
+
+ v = le16_to_cpu(es->s_want_extra_isize);
+ if (v > max) {
+ ext4_msg(sb, KERN_ERR,
+ "bad s_want_extra_isize: %d", v);
+ goto failed_mount;
+ }
+ if (sbi->s_want_extra_isize < v)
+ sbi->s_want_extra_isize = v;
+
+ v = le16_to_cpu(es->s_min_extra_isize);
+ if (v > max) {
+ ext4_msg(sb, KERN_ERR,
+ "bad s_min_extra_isize: %d", v);
+ goto failed_mount;
+ }
+ if (sbi->s_want_extra_isize < v)
+ sbi->s_want_extra_isize = v;
+ }
+ }
+
if (sbi->s_es->s_mount_opts[0]) {
char *s_mount_opts = kstrndup(sbi->s_es->s_mount_opts,
sizeof(sbi->s_es->s_mount_opts),
@@ -4019,42 +4054,6 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
has_huge_files);
sb->s_maxbytes = ext4_max_size(sb->s_blocksize_bits, has_huge_files);

- if (le32_to_cpu(es->s_rev_level) == EXT4_GOOD_OLD_REV) {
- sbi->s_inode_size = EXT4_GOOD_OLD_INODE_SIZE;
- sbi->s_first_ino = EXT4_GOOD_OLD_FIRST_INO;
- } else {
- sbi->s_inode_size = le16_to_cpu(es->s_inode_size);
- sbi->s_first_ino = le32_to_cpu(es->s_first_ino);
- if (sbi->s_first_ino < EXT4_GOOD_OLD_FIRST_INO) {
- ext4_msg(sb, KERN_ERR, "invalid first ino: %u",
- sbi->s_first_ino);
- goto failed_mount;
- }
- if ((sbi->s_inode_size < EXT4_GOOD_OLD_INODE_SIZE) ||
- (!is_power_of_2(sbi->s_inode_size)) ||
- (sbi->s_inode_size > blocksize)) {
- ext4_msg(sb, KERN_ERR,
- "unsupported inode size: %d",
- sbi->s_inode_size);
- goto failed_mount;
- }
- /*
- * i_atime_extra is the last extra field available for [acm]times in
- * struct ext4_inode. Checking for that field should suffice to ensure
- * we have extra space for all three.
- */
- if (sbi->s_inode_size >= offsetof(struct ext4_inode, i_atime_extra) +
- sizeof(((struct ext4_inode *)0)->i_atime_extra)) {
- sb->s_time_gran = 1;
- sb->s_time_max = EXT4_EXTRA_TIMESTAMP_MAX;
- } else {
- sb->s_time_gran = NSEC_PER_SEC;
- sb->s_time_max = EXT4_NON_EXTRA_TIMESTAMP_MAX;
- }
-
- sb->s_time_min = EXT4_TIMESTAMP_MIN;
- }
-
sbi->s_desc_size = le16_to_cpu(es->s_desc_size);
if (ext4_has_feature_64bit(sb)) {
if (sbi->s_desc_size < EXT4_MIN_DESC_SIZE_64BIT ||
@@ -4503,8 +4502,6 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
} else if (ret)
goto failed_mount4a;

- ext4_clamp_want_extra_isize(sb);
-
ext4_set_resv_clusters(sb);

err = ext4_setup_system_zone(sb);
@@ -5292,8 +5289,6 @@ static int ext4_remount(struct super_block *sb, int *flags, char *data)
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 "
--
2.24.1
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