KASAN: use-after-free Read in ext4_xattr_set_entry (2)

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: fb1c592cf4c9 Merge tag 'char-misc-4.19-rc7' of git://git.k..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11431406400000
kernel config: https://syzkaller.appspot.com/x/.config?x=c0af03fe452b65fb
dashboard link: https://syzkaller.appspot.com/bug?extid=4a39a025912b265cacef
compiler: gcc (GCC) 8.0.1 20180413 (experimental)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+4a39a0...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in ext4_xattr_set_entry+0x2f6a/0x3d70
fs/ext4/xattr.c:1600
Read of size 4 at addr ffff8801a4db491b by task syz-executor0/14364

CPU: 1 PID: 14364 Comm: syz-executor0 Not tainted 4.19.0-rc6+ #51
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x1c4/0x2b4 lib/dump_stack.c:113
print_address_description.cold.8+0x9/0x1ff mm/kasan/report.c:256
kasan_report_error mm/kasan/report.c:354 [inline]
kasan_report.cold.9+0x242/0x309 mm/kasan/report.c:412
__asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:432
ext4_xattr_set_entry+0x2f6a/0x3d70 fs/ext4/xattr.c:1600
ext4_xattr_ibody_set+0x8a/0x2c0 fs/ext4/xattr.c:2240
ext4_xattr_set_handle+0xb8f/0x1650 fs/ext4/xattr.c:2394
ext4_initxattrs+0xbd/0x120 fs/ext4/xattr_security.c:43
security_inode_init_security+0x1d1/0x3d0 security/security.c:502
ext4_init_security+0x34/0x40 fs/ext4/xattr_security.c:57
__ext4_new_inode+0x4a6a/0x65b0 fs/ext4/ialloc.c:1160
ext4_symlink+0x4b7/0x1130 fs/ext4/namei.c:3093
vfs_symlink+0x37a/0x5d0 fs/namei.c:4127
do_symlinkat+0x242/0x2d0 fs/namei.c:4154
__do_sys_symlink fs/namei.c:4173 [inline]
__se_sys_symlink fs/namei.c:4171 [inline]
__x64_sys_symlink+0x59/0x80 fs/namei.c:4171
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4572a7
Code: 64 8b 5d 00 e9 14 fd ff ff 4c 8b 74 24 30 64 c7 45 00 22 00 00 00 bb
22 00 00 00 e9 fd fc ff ff 0f 1f 00 b8 58 00 00 00 0f 05 <48> 3d 01 f0 ff
ff 0f 83 bd b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffcaac01628 EFLAGS: 00000206 ORIG_RAX: 0000000000000058
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00000000004572a7
RDX: 00007ffcaac016a7 RSI: 00000000004bcfd0 RDI: 00007ffcaac01690
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000017
R10: 0000000000000075 R11: 0000000000000206 R12: 0000000000000000
R13: 0000000000000001 R14: 0000000000000b01 R15: 0000000000000000

The buggy address belongs to the page:
page:ffffea0006936d00 count:0 mapcount:0 mapping:0000000000000000 index:0x1
flags: 0x2fffc0000000000()
raw: 02fffc0000000000 dead000000000100 dead000000000200 0000000000000000
raw: 0000000000000001 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8801a4db4800: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
ffff8801a4db4880: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> ffff8801a4db4900: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
^
ffff8801a4db4980: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
ffff8801a4db4a00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
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syzbot will keep track of this bug report. See:
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syzbot.

[syzbot]

syzbot has found a reproducer for the following crash on:

HEAD commit: ae4b064e Merge tag 'afs-fixes-20191211' of git://git.kerne..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=137f6499e00000
kernel config: https://syzkaller.appspot.com/x/.config?x=79f79de2a27d3e3d
dashboard link: https://syzkaller.appspot.com/bug?extid=4a39a025912b265cacef
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=15ec1332e00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=163455dee00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+4a39a0...@syzkaller.appspotmail.com

EXT4-fs error (device sda1): ext4_xattr_set_entry:1583: inode #2339: comm
syz-executor117: corrupted xattr entries
==================================================================
BUG: KASAN: use-after-free in ext4_xattr_set_entry+0x35de/0x3770
fs/ext4/xattr.c:1580
Read of size 4 at addr ffff888093705283 by task syz-executor117/9665

CPU: 0 PID: 9665 Comm: syz-executor117 Not tainted 5.5.0-rc1-syzkaller #0

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]

dump_stack+0x197/0x210 lib/dump_stack.c:118
print_address_description.constprop.0.cold+0xd4/0x30b mm/kasan/report.c:374
__kasan_report.cold+0x1b/0x41 mm/kasan/report.c:506
kasan_report+0x12/0x20 mm/kasan/common.c:639
__asan_report_load4_noabort+0x14/0x20 mm/kasan/generic_report.c:134
ext4_xattr_set_entry+0x35de/0x3770 fs/ext4/xattr.c:1580
ext4_xattr_ibody_set+0x80/0x2d0 fs/ext4/xattr.c:2216
ext4_xattr_set_handle+0x933/0x1200 fs/ext4/xattr.c:2372
ext4_initxattrs+0xc0/0x130 fs/ext4/xattr_security.c:43
security_inode_init_security security/security.c:996 [inline]
security_inode_init_security+0x2c8/0x3b0 security/security.c:969
ext4_init_security+0x34/0x40 fs/ext4/xattr_security.c:57
__ext4_new_inode+0x4288/0x4f30 fs/ext4/ialloc.c:1155
ext4_mkdir+0x3d5/0xe20 fs/ext4/namei.c:2774
vfs_mkdir+0x42e/0x670 fs/namei.c:3819
do_mkdirat+0x234/0x2a0 fs/namei.c:3842
__do_sys_mkdir fs/namei.c:3858 [inline]
__se_sys_mkdir fs/namei.c:3856 [inline]
__x64_sys_mkdir+0x5c/0x80 fs/namei.c:3856
do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x44d177
Code: 1f 40 00 b8 5a 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 4d d6 fb ff c3
66 2e 0f 1f 84 00 00 00 00 00 66 90 b8 53 00 00 00 0f 05 <48> 3d 01 f0 ff
ff 0f 83 2d d6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f5c9599fb18 EFLAGS: 00000246 ORIG_RAX: 0000000000000053
RAX: ffffffffffffffda RBX: 00000000006e69c8 RCX: 000000000044d177
RDX: 0000000000000003 RSI: 00000000000001ff RDI: 0000000020000000
RBP: 00000000006e69c0 R08: 0000000000000000 R09: 000000000000000a
R10: 0000000000000075 R11: 0000000000000246 R12: 00000000006e69cc
R13: 00007ffd790837cf R14: 00007f5c959a09c0 R15: 0000000000000000

The buggy address belongs to the page:

page:ffffea00024dc140 refcount:0 mapcount:0 mapping:0000000000000000
index:0x1
raw: 00fffe0000000000 ffffea0002183608 ffffea00027ef508 0000000000000000

raw: 0000000000000001 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:

ffff888093705180: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
ffff888093705200: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> ffff888093705280: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
^
ffff888093705300: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
ffff888093705380: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================

[syzbot]

syzbot has bisected this bug to:

commit 8835cae5f2abd7f7a3143afe357f416aff5517a4
Author: Chris Lapa <ch...@lapa.com.au>
Date: Wed Jan 11 01:44:47 2017 +0000

power: supply: bq27xxx: adds specific support for bq27520-g4 revision.

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=16661f41e00000
start commit: ae4b064e Merge tag 'afs-fixes-20191211' of git://git.kerne..
git tree: upstream
final crash: https://syzkaller.appspot.com/x/report.txt?x=15661f41e00000
console output: https://syzkaller.appspot.com/x/log.txt?x=11661f41e00000

kernel config: https://syzkaller.appspot.com/x/.config?x=79f79de2a27d3e3d
dashboard link: https://syzkaller.appspot.com/bug?extid=4a39a025912b265cacef

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=15ec1332e00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=163455dee00000

Reported-by: syzbot+4a39a0...@syzkaller.appspotmail.com
Fixes: 8835cae5f2ab ("power: supply: bq27xxx: adds specific support for
bq27520-g4 revision.")

For information about bisection process see: https://goo.gl/tpsmEJ#bisection

[Theodore Y. Ts'o]

On Sat, Dec 14, 2019 at 05:27:00PM -0800, syzbot wrote:
> syzbot has bisected this bug to:
>
> commit 8835cae5f2abd7f7a3143afe357f416aff5517a4
> Author: Chris Lapa <ch...@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 <ty...@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 <ty...@mit.edu>
Reported-by: syzbot+4a39a0...@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

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger
crash:

Reported-and-tested-by:
syzbot+4a39a0...@syzkaller.appspotmail.com

Tested on:

commit: dfdeeb41 Merge branch 'tt/misc' into dev
git tree:
https://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4.git master
kernel config: https://syzkaller.appspot.com/x/.config?x=be3b077056d26622

dashboard link: https://syzkaller.appspot.com/bug?extid=4a39a025912b265cacef
compiler: gcc (GCC) 9.0.0 20181231 (experimental)

patch: https://syzkaller.appspot.com/x/patch.diff?x=11b02546e00000

Note: testing is done by a robot and is best-effort only.

[Dmitry Vyukov]

On Sun, Dec 15, 2019 at 7:30 AM Theodore Y. Ts'o <ty...@mit.edu> wrote:
>
> On Sat, Dec 14, 2019 at 05:27:00PM -0800, syzbot wrote:
> > syzbot has bisected this bug to:
> >
> > commit 8835cae5f2abd7f7a3143afe357f416aff5517a4
> > Author: Chris Lapa <ch...@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.

Agree.

FTR, it seems that bisection was first diverged by this kernel bug:

testing commit 8835cae5f2abd7f7a3143afe357f416aff5517a4 with gcc (GCC) 5.5.0
run #0: crashed: WARNING in batadv_mcast_mla_update

on top of this non-deterministic kernel build bug kicked in to prevent
detection of "culprit does not affect build":

culprit signature: 2aca06cd9a4175f124f866fe66467cfa96c0bf2a
parent signature: 8a8dd9ca5726f129b6d36eb6e1f3b78cc7c18b31

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