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 jfs_ioc_trim) 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: [email protected]
Signed-off-by: Edward Adam Davis <[email protected]>
Signed-off-by: Dave Kleikamp <[email protected]>

Author: ea1davis

fs/jfs/jfs_discard.c

@@ -65,7 +65,7 @@ void jfs_issue_discard(struct inode *ip, u64 blkno, u64 nblocks)
 int jfs_ioc_trim(struct inode *ip, struct fstrim_range *range)
 {
 	struct inode *ipbmap = JFS_SBI(ip->i_sb)->ipbmap;
-	struct bmap *bmp = JFS_SBI(ip->i_sb)->bmap;
+	struct bmap *bmp;
 	struct super_block *sb = ipbmap->i_sb;
 	int agno, agno_end;
 	u64 start, end, minlen;
@@ -83,10 +83,15 @@ int jfs_ioc_trim(struct inode *ip, struct fstrim_range *range)
 	if (minlen == 0)
 		minlen = 1;
 
+	down_read(&sb->s_umount);
+	bmp = JFS_SBI(ip->i_sb)->bmap;
+
 	if (minlen > bmp->db_agsize ||
 	    start >= bmp->db_mapsize ||
-	    range->len < sb->s_blocksize)
+	    range->len < sb->s_blocksize) {
+		up_read(&sb->s_umount);
 		return -EINVAL;
+	}
 
 	if (end >= bmp->db_mapsize)
 		end = bmp->db_mapsize - 1;
@@ -100,6 +105,8 @@ int jfs_ioc_trim(struct inode *ip, struct fstrim_range *range)
 		trimmed += dbDiscardAG(ip, agno, minlen);
 		agno++;
 	}
+
+	up_read(&sb->s_umount);
 	range->len = trimmed << sb->s_blocksize_bits;
 
 	return 0;