linux-kernel - [PATCH] jfs: Fix uaf in dbFreeBits

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Message-ID: <tencent_964B0C7439761367DC3D5337CA968C369E09@qq.com>
Date: Sat, 17 Aug 2024 11:55:31 +0800
From: Edward Adam Davis <eadavis@...com>
To: syzbot+3c010e21296f33a5dc16@...kaller.appspotmail.com
Cc: jfs-discussion@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org,
	shaggy@...nel.org,
	syzkaller-bugs@...glegroups.com
Subject: [PATCH] jfs: Fix uaf in dbFreeBits

[syzbot reported]
==================================================================
BUG: KASAN: slab-use-after-free in __mutex_lock_common kernel/locking/mutex.c:587 [inline]
BUG: KASAN: slab-use-after-free in __mutex_lock+0xfe/0xd70 kernel/locking/mutex.c:752
Read of size 8 at addr ffff8880229254b0 by task syz-executor357/5216

CPU: 0 UID: 0 PID: 5216 Comm: syz-executor357 Not tainted 6.11.0-rc3-syzkaller-00156-gd7a5aa4b3c00 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/27/2024
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:93 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:119
 print_address_description mm/kasan/report.c:377 [inline]
 print_report+0x169/0x550 mm/kasan/report.c:488
 kasan_report+0x143/0x180 mm/kasan/report.c:601
 __mutex_lock_common kernel/locking/mutex.c:587 [inline]
 __mutex_lock+0xfe/0xd70 kernel/locking/mutex.c:752
 dbFreeBits+0x7ea/0xd90 fs/jfs/jfs_dmap.c:2390
 dbFreeDmap fs/jfs/jfs_dmap.c:2089 [inline]
 dbFree+0x35b/0x680 fs/jfs/jfs_dmap.c:409
 dbDiscardAG+0x8a9/0xa20 fs/jfs/jfs_dmap.c:1650
 jfs_ioc_trim+0x433/0x670 fs/jfs/jfs_discard.c:100
 jfs_ioctl+0x2d0/0x3e0 fs/jfs/ioctl.c:131
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:907 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:893
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83

Freed by task 5218:
 kasan_save_stack mm/kasan/common.c:47 [inline]
 kasan_save_track+0x3f/0x80 mm/kasan/common.c:68
 kasan_save_free_info+0x40/0x50 mm/kasan/generic.c:579
 poison_slab_object+0xe0/0x150 mm/kasan/common.c:240
 __kasan_slab_free+0x37/0x60 mm/kasan/common.c:256
 kasan_slab_free include/linux/kasan.h:184 [inline]
 slab_free_hook mm/slub.c:2252 [inline]
 slab_free mm/slub.c:4473 [inline]
 kfree+0x149/0x360 mm/slub.c:4594
 dbUnmount+0x11d/0x190 fs/jfs/jfs_dmap.c:278
 jfs_mount_rw+0x4ac/0x6a0 fs/jfs/jfs_mount.c:247
 jfs_remount+0x3d1/0x6b0 fs/jfs/super.c:454
 reconfigure_super+0x445/0x880 fs/super.c:1083
 vfs_cmd_reconfigure fs/fsopen.c:263 [inline]
 vfs_fsconfig_locked fs/fsopen.c:292 [inline]
 __do_sys_fsconfig fs/fsopen.c:473 [inline]
 __se_sys_fsconfig+0xb6e/0xf80 fs/fsopen.c:345
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f 

[Analysis] 
There are two paths (dbUnmount and dbDiscardAG) that generate race
condition when accessing bmap, which leads to the occurrence of uaf.

Use the lock s_umount to synchronize them, in order to avoid uaf caused
by race condition.

Reported-and-tested-by: syzbot+3c010e21296f33a5dc16@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=3c010e21296f33a5dc16
Signed-off-by: Edward Adam Davis <eadavis@...com>
---
 fs/jfs/jfs_dmap.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c
index cb3cda1390ad..a409ae18454a 100644
--- a/fs/jfs/jfs_dmap.c
+++ b/fs/jfs/jfs_dmap.c
@@ -1645,7 +1645,9 @@ s64 dbDiscardAG(struct inode *ip, int agno, s64 minlen)
 		 * call jfs_issue_discard() itself */
 		if (!(JFS_SBI(sb)->flag & JFS_DISCARD))
 			jfs_issue_discard(ip, tt->blkno, tt->nblocks);
+		down_read(&sb->s_umount);
 		dbFree(ip, tt->blkno, tt->nblocks);
+		up_read(&sb->s_umount);
 		trimmed += tt->nblocks;
 	}
 	kfree(totrim);
-- 
2.43.0