Message-ID: <20250708095339.3079788-1-chao@kernel.org>
Date: Tue,  8 Jul 2025 17:53:39 +0800
From: Chao Yu <chao@...nel.org>
To: jaegeuk@...nel.org
Cc: linux-f2fs-devel@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org,
	Chao Yu <chao@...nel.org>
Subject: [PATCH v2] f2fs: fix to avoid UAF in f2fs_sync_inode_meta()

syzbot reported an UAF issue as below: [1] [2]

[1] https://syzkaller.appspot.com/text?tag=CrashReport&x=16594c60580000

==================================================================
BUG: KASAN: use-after-free in __list_del_entry_valid+0xa6/0x130 lib/list_debug.c:62
Read of size 8 at addr ffff888100567dc8 by task kworker/u4:0/8

CPU: 1 PID: 8 Comm: kworker/u4:0 Tainted: G        W          6.1.129-syzkaller-00017-g642656a36791 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
Workqueue: writeback wb_workfn (flush-7:0)
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x151/0x1b7 lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:316 [inline]
 print_report+0x158/0x4e0 mm/kasan/report.c:427
 kasan_report+0x13c/0x170 mm/kasan/report.c:531
 __asan_report_load8_noabort+0x14/0x20 mm/kasan/report_generic.c:351
 __list_del_entry_valid+0xa6/0x130 lib/list_debug.c:62
 __list_del_entry include/linux/list.h:134 [inline]
 list_del_init include/linux/list.h:206 [inline]
 f2fs_inode_synced+0x100/0x2e0 fs/f2fs/super.c:1553
 f2fs_update_inode+0x72/0x1c40 fs/f2fs/inode.c:588
 f2fs_update_inode_page+0x135/0x170 fs/f2fs/inode.c:706
 f2fs_write_inode+0x416/0x790 fs/f2fs/inode.c:734
 write_inode fs/fs-writeback.c:1460 [inline]
 __writeback_single_inode+0x4cf/0xb80 fs/fs-writeback.c:1677
 writeback_sb_inodes+0xb32/0x1910 fs/fs-writeback.c:1903
 __writeback_inodes_wb+0x118/0x3f0 fs/fs-writeback.c:1974
 wb_writeback+0x3da/0xa00 fs/fs-writeback.c:2081
 wb_check_background_flush fs/fs-writeback.c:2151 [inline]
 wb_do_writeback fs/fs-writeback.c:2239 [inline]
 wb_workfn+0xbba/0x1030 fs/fs-writeback.c:2266
 process_one_work+0x73d/0xcb0 kernel/workqueue.c:2299
 worker_thread+0xa60/0x1260 kernel/workqueue.c:2446
 kthread+0x26d/0x300 kernel/kthread.c:386
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
 </TASK>

Allocated by task 298:
 kasan_save_stack mm/kasan/common.c:45 [inline]
 kasan_set_track+0x4b/0x70 mm/kasan/common.c:52
 kasan_save_alloc_info+0x1f/0x30 mm/kasan/generic.c:505
 __kasan_slab_alloc+0x6c/0x80 mm/kasan/common.c:333
 kasan_slab_alloc include/linux/kasan.h:202 [inline]
 slab_post_alloc_hook+0x53/0x2c0 mm/slab.h:768
 slab_alloc_node mm/slub.c:3421 [inline]
 slab_alloc mm/slub.c:3431 [inline]
 __kmem_cache_alloc_lru mm/slub.c:3438 [inline]
 kmem_cache_alloc_lru+0x102/0x270 mm/slub.c:3454
 alloc_inode_sb include/linux/fs.h:3255 [inline]
 f2fs_alloc_inode+0x2d/0x350 fs/f2fs/super.c:1437
 alloc_inode fs/inode.c:261 [inline]
 iget_locked+0x18c/0x7e0 fs/inode.c:1373
 f2fs_iget+0x55/0x4ca0 fs/f2fs/inode.c:486
 f2fs_lookup+0x3c1/0xb50 fs/f2fs/namei.c:484
 __lookup_slow+0x2b9/0x3e0 fs/namei.c:1689
 lookup_slow+0x5a/0x80 fs/namei.c:1706
 walk_component+0x2e7/0x410 fs/namei.c:1997
 lookup_last fs/namei.c:2454 [inline]
 path_lookupat+0x16d/0x450 fs/namei.c:2478
 filename_lookup+0x251/0x600 fs/namei.c:2507
 vfs_statx+0x107/0x4b0 fs/stat.c:229
 vfs_fstatat fs/stat.c:267 [inline]
 vfs_lstat include/linux/fs.h:3434 [inline]
 __do_sys_newlstat fs/stat.c:423 [inline]
 __se_sys_newlstat+0xda/0x7c0 fs/stat.c:417
 __x64_sys_newlstat+0x5b/0x70 fs/stat.c:417
 x64_sys_call+0x52/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:7
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x3b/0x80 arch/x86/entry/common.c:81
 entry_SYSCALL_64_after_hwframe+0x68/0xd2

Freed by task 0:
 kasan_save_stack mm/kasan/common.c:45 [inline]
 kasan_set_track+0x4b/0x70 mm/kasan/common.c:52
 kasan_save_free_info+0x2b/0x40 mm/kasan/generic.c:516
 ____kasan_slab_free+0x131/0x180 mm/kasan/common.c:241
 __kasan_slab_free+0x11/0x20 mm/kasan/common.c:249
 kasan_slab_free include/linux/kasan.h:178 [inline]
 slab_free_hook mm/slub.c:1745 [inline]
 slab_free_freelist_hook mm/slub.c:1771 [inline]
 slab_free mm/slub.c:3686 [inline]
 kmem_cache_free+0x291/0x560 mm/slub.c:3711
 f2fs_free_inode+0x24/0x30 fs/f2fs/super.c:1584
 i_callback+0x4b/0x70 fs/inode.c:250
 rcu_do_batch+0x552/0xbe0 kernel/rcu/tree.c:2297
 rcu_core+0x502/0xf40 kernel/rcu/tree.c:2557
 rcu_core_si+0x9/0x10 kernel/rcu/tree.c:2574
 handle_softirqs+0x1db/0x650 kernel/softirq.c:624
 __do_softirq kernel/softirq.c:662 [inline]
 invoke_softirq kernel/softirq.c:479 [inline]
 __irq_exit_rcu+0x52/0xf0 kernel/softirq.c:711
 irq_exit_rcu+0x9/0x10 kernel/softirq.c:723
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1118 [inline]
 sysvec_apic_timer_interrupt+0xa9/0xc0 arch/x86/kernel/apic/apic.c:1118
 asm_sysvec_apic_timer_interrupt+0x1b/0x20 arch/x86/include/asm/idtentry.h:691

Last potentially related work creation:
 kasan_save_stack+0x3b/0x60 mm/kasan/common.c:45
 __kasan_record_aux_stack+0xb4/0xc0 mm/kasan/generic.c:486
 kasan_record_aux_stack_noalloc+0xb/0x10 mm/kasan/generic.c:496
 __call_rcu_common kernel/rcu/tree.c:2807 [inline]
 call_rcu+0xdc/0x10f0 kernel/rcu/tree.c:2926
 destroy_inode fs/inode.c:316 [inline]
 evict+0x87d/0x930 fs/inode.c:720
 iput_final fs/inode.c:1834 [inline]
 iput+0x616/0x690 fs/inode.c:1860
 do_unlinkat+0x4e1/0x920 fs/namei.c:4396
 __do_sys_unlink fs/namei.c:4437 [inline]
 __se_sys_unlink fs/namei.c:4435 [inline]
 __x64_sys_unlink+0x49/0x50 fs/namei.c:4435
 x64_sys_call+0x289/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:88
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x3b/0x80 arch/x86/entry/common.c:81
 entry_SYSCALL_64_after_hwframe+0x68/0xd2

The buggy address belongs to the object at ffff888100567a10
 which belongs to the cache f2fs_inode_cache of size 1360
The buggy address is located 952 bytes inside of
 1360-byte region [ffff888100567a10, ffff888100567f60)

The buggy address belongs to the physical page:
page:ffffea0004015800 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x100560
head:ffffea0004015800 order:3 compound_mapcount:0 compound_pincount:0
flags: 0x4000000000010200(slab|head|zone=1)
raw: 4000000000010200 0000000000000000 dead000000000122 ffff8881002c4d80
raw: 0000000000000000 0000000080160016 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Reclaimable, gfp_mask 0xd2050(__GFP_IO|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC|__GFP_RECLAIMABLE), pid 298, tgid 298 (syz-executor330), ts 26489303743, free_ts 0
 set_page_owner include/linux/page_owner.h:33 [inline]
 post_alloc_hook+0x213/0x220 mm/page_alloc.c:2637
 prep_new_page+0x1b/0x110 mm/page_alloc.c:2644
 get_page_from_freelist+0x3a98/0x3b10 mm/page_alloc.c:4539
 __alloc_pages+0x234/0x610 mm/page_alloc.c:5837
 alloc_slab_page+0x6c/0xf0 include/linux/gfp.h:-1
 allocate_slab mm/slub.c:1962 [inline]
 new_slab+0x90/0x3e0 mm/slub.c:2015
 ___slab_alloc+0x6f9/0xb80 mm/slub.c:3203
 __slab_alloc+0x5d/0xa0 mm/slub.c:3302
 slab_alloc_node mm/slub.c:3387 [inline]
 slab_alloc mm/slub.c:3431 [inline]
 __kmem_cache_alloc_lru mm/slub.c:3438 [inline]
 kmem_cache_alloc_lru+0x149/0x270 mm/slub.c:3454
 alloc_inode_sb include/linux/fs.h:3255 [inline]
 f2fs_alloc_inode+0x2d/0x350 fs/f2fs/super.c:1437
 alloc_inode fs/inode.c:261 [inline]
 iget_locked+0x18c/0x7e0 fs/inode.c:1373
 f2fs_iget+0x55/0x4ca0 fs/f2fs/inode.c:486
 f2fs_fill_super+0x5360/0x6dc0 fs/f2fs/super.c:4488
 mount_bdev+0x282/0x3b0 fs/super.c:1445
 f2fs_mount+0x34/0x40 fs/f2fs/super.c:4743
 legacy_get_tree+0xf1/0x190 fs/fs_context.c:632
page_owner free stack trace missing

Memory state around the buggy address:
 ffff888100567c80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888100567d00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff888100567d80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                              ^
 ffff888100567e00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888100567e80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

[2] https://syzkaller.appspot.com/text?tag=CrashLog&x=13654c60580000

[   24.675720][   T28] audit: type=1400 audit(1745327318.732:72): avc:  denied  { write } for  pid=298 comm="syz-executor399" name="/" dev="loop0" ino=3 scontext=root:sysadm_r:sysadm_t tcontext=system_u:object_r:unlabeled_t tclass=dir permissive=1
[   24.705426][  T296] ------------[ cut here ]------------
[   24.706608][   T28] audit: type=1400 audit(1745327318.732:73): avc:  denied  { remove_name } for  pid=298 comm="syz-executor399" name="file0" dev="loop0" ino=4 scontext=root:sysadm_r:sysadm_t tcontext=system_u:object_r:unlabeled_t tclass=dir permissive=1
[   24.711550][  T296] WARNING: CPU: 0 PID: 296 at fs/f2fs/inode.c:847 f2fs_evict_inode+0x1262/0x1540
[   24.734141][   T28] audit: type=1400 audit(1745327318.732:74): avc:  denied  { rename } for  pid=298 comm="syz-executor399" name="file0" dev="loop0" ino=4 scontext=root:sysadm_r:sysadm_t tcontext=system_u:object_r:unlabeled_t tclass=dir permissive=1
[   24.742969][  T296] Modules linked in:
[   24.765201][   T28] audit: type=1400 audit(1745327318.732:75): avc:  denied  { add_name } for  pid=298 comm="syz-executor399" name="bus" scontext=root:sysadm_r:sysadm_t tcontext=system_u:object_r:unlabeled_t tclass=dir permissive=1
[   24.768847][  T296] CPU: 0 PID: 296 Comm: syz-executor399 Not tainted 6.1.129-syzkaller-00017-g642656a36791 #0
[   24.799506][  T296] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
[   24.809401][  T296] RIP: 0010:f2fs_evict_inode+0x1262/0x1540
[   24.815018][  T296] Code: 34 70 4a ff eb 0d e8 2d 70 4a ff 4d 89 e5 4c 8b 64 24 18 48 8b 5c 24 28 4c 89 e7 e8 78 38 03 00 e9 84 fc ff ff e8 0e 70 4a ff <0f> 0b 4c 89 f7 be 08 00 00 00 e8 7f 21 92 ff f0 41 80 0e 04 e9 61
[   24.834584][  T296] RSP: 0018:ffffc90000db7a40 EFLAGS: 00010293
[   24.840465][  T296] RAX: ffffffff822aca42 RBX: 0000000000000002 RCX: ffff888110948000
[   24.848291][  T296] RDX: 0000000000000000 RSI: 0000000000000002 RDI: 0000000000000000
[   24.856064][  T296] RBP: ffffc90000db7bb0 R08: ffffffff822ac6a8 R09: ffffed10200b005d
[   24.864073][  T296] R10: 0000000000000000 R11: dffffc0000000001 R12: ffff888100580000
[   24.871812][  T296] R13: dffffc0000000000 R14: ffff88810fef4078 R15: 1ffff920001b6f5c

The root cause is w/ a fuzzed image, f2fs may missed to clear FI_DIRTY_INODE
flag for target inode, after f2fs_evict_inode(), the inode is still linked in
sbi->inode_list[DIRTY_META] global list, once it triggers checkpoint,
f2fs_sync_inode_meta() may access the released inode.

In f2fs_evict_inode(), let's always call f2fs_inode_synced() to clear
FI_DIRTY_INODE flag and drop inode from global dirty list to avoid this
UAF issue.

Fixes: 0f18b462b2e5 ("f2fs: flush inode metadata when checkpoint is doing")
Closes: https://syzkaller.appspot.com/bug?extid=849174b2efaf0d8be6ba
Signed-off-by: Chao Yu <chao@...nel.org>
---
v2:
- add fixes line, commit 0f18b462b2e5 ("f2fs: flush inode metadata when
checkpoint is doing") missed to call f2fs_inode_synced() to avoid any
corner case when CONFIG_F2FS_CHECK_FS is off and inode is dirty.
 fs/f2fs/inode.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
index 083d52a42bfb..d3c6f3202b69 100644
--- a/fs/f2fs/inode.c
+++ b/fs/f2fs/inode.c
@@ -949,8 +949,12 @@ void f2fs_evict_inode(struct inode *inode)
 	if (likely(!f2fs_cp_error(sbi) &&
 				!is_sbi_flag_set(sbi, SBI_CP_DISABLED)))
 		f2fs_bug_on(sbi, is_inode_flag_set(inode, FI_DIRTY_INODE));
-	else
-		f2fs_inode_synced(inode);
+
+	/*
+	 * anyway, it needs to remove the inode from sbi->inode_list[DIRTY_META]
+	 * list to avoid UAF in f2fs_sync_inode_meta() during checkpoint.
+	 */
+	f2fs_inode_synced(inode);
 
 	/* for the case f2fs_new_inode() was failed, .i_ino is zero, skip it */
 	if (inode->i_ino)
-- 
2.49.0

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