[syzbot] [f2fs?] kernel BUG in f2fs_write_end_io (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: aa54b1d27fe0 rxrpc: Also unshare DATA/RESPONSE packets whe..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14adabce580000
kernel config: https://syzkaller.appspot.com/x/.config?x=f2e8ebfec4636d32
dashboard link: https://syzkaller.appspot.com/bug?extid=4af46ee83100e99bce09
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1643c3ce580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=12adabce580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/418e3ed628cf/disk-aa54b1d2.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/a35b53d0ab2f/vmlinux-aa54b1d2.xz
kernel image: https://storage.googleapis.com/syzbot-assets/03c3fa0081b4/bzImage-aa54b1d2.xz
mounted in repro #1: https://storage.googleapis.com/syzbot-assets/13e397c7f935/mount_0.gz
fsck result: failed (log: https://syzkaller.appspot.com/x/fsck.log?x=158fad06580000)
mounted in repro #2: https://storage.googleapis.com/syzbot-assets/2f91edde40dc/mount_8.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+4af46e...@syzkaller.appspotmail.com

------------[ cut here ]------------
kernel BUG at fs/f2fs/data.c:388!
Oops: invalid opcode: 0000 [#1] SMP KASAN PTI
CPU: 1 UID: 0 PID: 31 Comm: ksoftirqd/1 Not tainted syzkaller #0 PREEMPT_{RT,(full)}
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
RIP: 0010:f2fs_write_end_io+0x16df/0x1740 fs/f2fs/data.c:388
Code: 20 3c 9b 8b e8 12 0a f7 fc 90 0f 0b e8 0a cc 93 fd 48 8b 3c 24 48 c7 c6 20 3c 9b 8b e8 fa 09 f7 fc 90 0f 0b e8 f2 cb 93 fd 90 <0f> 0b e8 ea cb 93 fd 48 8b 3c 24 48 c7 c6 20 3c 9b 8b e8 da 09 f7
RSP: 0018:ffffc90000a5fb18 EFLAGS: 00010246
RAX: ffffffff8430aade RBX: ffffea0000d91c40 RCX: ffff88801d6b0000
RDX: 0000000000000100 RSI: 0000000000000000 RDI: 0000000000000100
RBP: dffffc0000000000 R08: 0000000000000000 R09: 0000000000000100
R10: dffffc0000000000 R11: fffffbfff1f11dff R12: 0000000036471000
R13: ffffea0000d91c80 R14: 000000000000000b R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff888126276000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007eff6352cff8 CR3: 000000002caa2000 CR4: 00000000003526f0
Call Trace:
<TASK>
blk_update_request+0x57e/0xe60 block/blk-mq.c:1016
blk_mq_end_request+0x3e/0x70 block/blk-mq.c:1178
blk_complete_reqs block/blk-mq.c:1253 [inline]
blk_done_softirq+0x10a/0x160 block/blk-mq.c:1258
handle_softirqs+0x1de/0x6d0 kernel/softirq.c:622
run_ksoftirqd+0x52/0x180 kernel/softirq.c:1076
smpboot_thread_fn+0x541/0xa50 kernel/smpboot.c:160
kthread+0x388/0x470 kernel/kthread.c:436
ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:f2fs_write_end_io+0x16df/0x1740 fs/f2fs/data.c:388
Code: 20 3c 9b 8b e8 12 0a f7 fc 90 0f 0b e8 0a cc 93 fd 48 8b 3c 24 48 c7 c6 20 3c 9b 8b e8 fa 09 f7 fc 90 0f 0b e8 f2 cb 93 fd 90 <0f> 0b e8 ea cb 93 fd 48 8b 3c 24 48 c7 c6 20 3c 9b 8b e8 da 09 f7
RSP: 0018:ffffc90000a5fb18 EFLAGS: 00010246
RAX: ffffffff8430aade RBX: ffffea0000d91c40 RCX: ffff88801d6b0000
RDX: 0000000000000100 RSI: 0000000000000000 RDI: 0000000000000100
RBP: dffffc0000000000 R08: 0000000000000000 R09: 0000000000000100
R10: dffffc0000000000 R11: fffffbfff1f11dff R12: 0000000036471000
R13: ffffea0000d91c80 R14: 000000000000000b R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff888126276000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007eff6352cff8 CR3: 000000002caa2000 CR4: 00000000003526f0


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

If you want to overwrite report's subsystems, reply with:
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(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-...@vger.kernel.org, syzkall...@googlegroups.com.

***

Subject: [PATCH] f2fs: DEBUG: trace node folio lifecycle to diagnose write_end_io BUG
Author: karti...@gmail.com

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master


Not for upstream. Instrumentation to identify which path leaves
a node folio with folio->index != nid_of_node(folio) at writeback
time, triggering the BUG in f2fs_write_end_io() reported by syzbot.

Adds pr_info trace points at:
- f2fs_new_node_folio() - in-memory node folio construction
- __get_node_folio() - node folio lookup (cache or read)
- __get_node_folio() - synchronous footer sanity failure
- f2fs_finish_read_bio() - async read completion footer check
- f2fs_write_end_io() - write completion footer check

BUG_ON in f2fs_write_end_io() is intentionally retained so the
kernel halts at the failing folio and the preceding pr_info
output appears in the syzbot console log.

Link: https://syzkaller.appspot.com/bug?extid=4af46ee83100e99bce09
Not-Signed-off-by: Deepanshu Kartikey <karti...@gmail.com>
---
fs/f2fs/data.c | 19 ++++++++++++++-----
fs/f2fs/node.c | 5 +++++
2 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 8d4f1e75dee3..dc01a4fe089a 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -174,10 +174,17 @@ static void f2fs_finish_read_bio(struct bio *bio, bool in_task)
dec_page_count(F2FS_F_SB(folio), __read_io_type(folio));

if (bio->bi_status == BLK_STS_OK &&
- F2FS_F_SB(folio)->node_inode && is_node_folio(folio) &&
- f2fs_sanity_check_node_footer(F2FS_F_SB(folio),
- folio, folio->index, NODE_TYPE_REGULAR, true))
- bio->bi_status = BLK_STS_IOERR;
+ F2FS_F_SB(folio)->node_inode && is_node_folio(folio)) {
+ int rc = f2fs_sanity_check_node_footer(F2FS_F_SB(folio),
+ folio, folio->index, NODE_TYPE_REGULAR, true);
+ pr_info("f2fs-dbg: READ end_io: index=%lu footer_nid=%u ino=%u rc=%d\n",
+ folio->index,
+ nid_of_node(folio),
+ ino_of_node(folio),
+ rc);
+ if (rc)
+ bio->bi_status = BLK_STS_IOERR;
+ }

if (finished)
folio_end_read(folio, bio->bi_status == BLK_STS_OK);
@@ -383,8 +390,10 @@ static void f2fs_write_end_io(struct bio *bio)
}

if (is_node_folio(folio)) {
- f2fs_sanity_check_node_footer(sbi, folio,
+ int rc = f2fs_sanity_check_node_footer(sbi, folio,
folio->index, NODE_TYPE_REGULAR, true);
+ pr_info("f2fs-dbg: WRITE end_io: index=%lu footer_nid=%u ino=%u rc=%d\n",
+ folio->index,nid_of_node(folio),ino_of_node(folio),rc);
f2fs_bug_on(sbi, folio->index != nid_of_node(folio));
}
if (f2fs_in_warm_node_list(folio))
diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
index 4e5bd9e4cfc3..12a9774ac1df 100644
--- a/fs/f2fs/node.c
+++ b/fs/f2fs/node.c
@@ -1423,6 +1423,8 @@ struct folio *f2fs_new_node_folio(struct dnode_of_data *dn, unsigned int ofs)
f2fs_folio_wait_writeback(folio, NODE, true, true);
fill_node_footer(folio, dn->nid, dn->inode->i_ino, ofs, true);
set_cold_node(folio, S_ISDIR(dn->inode->i_mode));
+ pr_info("f2fs-dbg: NEW node_folio: nid=%u ino=%lu ofs=%u\n",
+ dn->nid, dn->inode->i_ino, ofs);
if (!folio_test_uptodate(folio))
folio_mark_uptodate(folio);
if (folio_mark_dirty(folio))
@@ -1565,6 +1567,7 @@ static struct folio *__get_node_folio(struct f2fs_sb_info *sbi, pgoff_t nid,
struct folio *folio;
int err;

+ pr_info("f2fs-dbg: GET node_folio: nid=%lu ntype=%d\n", nid, ntype);
if (!nid)
return ERR_PTR(-ENOENT);
if (f2fs_check_nid_range(sbi, nid))
@@ -1603,6 +1606,8 @@ static struct folio *__get_node_folio(struct f2fs_sb_info *sbi, pgoff_t nid,
err = f2fs_sanity_check_node_footer(sbi, folio, nid, ntype, false);
if (!err)
return folio;
+ pr_info("f2fs-dbg: SYNC sanity fail: nid=%lu footer_nid=%u ino=%u err=%d\n",
+ nid,nid_of_node(folio),ino_of_node(folio),err);
out_err:
folio_clear_uptodate(folio);
out_put_err:
--
2.43.0

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
kernel BUG in f2fs_write_end_io

f2fs-dbg: WRITE end_io: index=11 footer_nid=0 ino=0 rc=-117
------------[ cut here ]------------
kernel BUG at fs/f2fs/data.c:397!

Oops: invalid opcode: 0000 [#1] SMP KASAN PTI

CPU: 0 UID: 0 PID: 15 Comm: ksoftirqd/0 Not tainted syzkaller #0 PREEMPT_{RT,(full)}

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026

RIP: 0010:f2fs_write_end_io+0x193e/0x1970 fs/f2fs/data.c:397
Code: c6 e0 3c 9b 8b e8 02 e5 f6 fc 90 0f 0b e8 8a c9 93 fd 4c 89 e7 48 c7 c6 00 3e 9b 8b e8 eb e4 f6 fc 90 0f 0b e8 73 c9 93 fd 90 <0f> 0b e8 6b c9 93 fd 48 8b 3c 24 48 c7 c6 e0 3c 9b 8b e8 cb e4 f6
RSP: 0018:ffffc90000147b08 EFLAGS: 00010246
RAX: ffffffff8430cfed RBX: 0000000000001000 RCX: ffff88801cee9ec0

RDX: 0000000000000100 RSI: 0000000000000000 RDI: 0000000000000100
RBP: dffffc0000000000 R08: 0000000000000000 R09: 0000000000000100

R10: dffffc0000000000 R11: fffff52000028f11 R12: ffffea0000a312c0
R13: 0000000000001000 R14: 000000000000000b R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff888126174000(0000) knlGS:0000000000000000

CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: 00007fa3d3ae7dac CR3: 0000000037e5c000 CR4: 00000000003526f0

Call Trace:
<TASK>
blk_update_request+0x57e/0xe60 block/blk-mq.c:1016
blk_mq_end_request+0x3e/0x70 block/blk-mq.c:1178
blk_complete_reqs block/blk-mq.c:1253 [inline]
blk_done_softirq+0x10a/0x160 block/blk-mq.c:1258
handle_softirqs+0x1de/0x6d0 kernel/softirq.c:622
run_ksoftirqd+0x52/0x180 kernel/softirq.c:1076
smpboot_thread_fn+0x541/0xa50 kernel/smpboot.c:160
kthread+0x388/0x470 kernel/kthread.c:436
ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---

RIP: 0010:f2fs_write_end_io+0x193e/0x1970 fs/f2fs/data.c:397
Code: c6 e0 3c 9b 8b e8 02 e5 f6 fc 90 0f 0b e8 8a c9 93 fd 4c 89 e7 48 c7 c6 00 3e 9b 8b e8 eb e4 f6 fc 90 0f 0b e8 73 c9 93 fd 90 <0f> 0b e8 6b c9 93 fd 48 8b 3c 24 48 c7 c6 e0 3c 9b 8b e8 cb e4 f6
RSP: 0018:ffffc90000147b08 EFLAGS: 00010246
RAX: ffffffff8430cfed RBX: 0000000000001000 RCX: ffff88801cee9ec0

RDX: 0000000000000100 RSI: 0000000000000000 RDI: 0000000000000100
RBP: dffffc0000000000 R08: 0000000000000000 R09: 0000000000000100

R10: dffffc0000000000 R11: fffff52000028f11 R12: ffffea0000a312c0
R13: 0000000000001000 R14: 000000000000000b R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff888126174000(0000) knlGS:0000000000000000

CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: 00007fa3d3ae7dac CR3: 0000000037e5c000 CR4: 00000000003526f0


Tested on:

commit: 66182ca8 Merge tag 'net-7.1-rc4' of git://git.kernel.o..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10c5e996580000

kernel config: https://syzkaller.appspot.com/x/.config?x=f2e8ebfec4636d32
dashboard link: https://syzkaller.appspot.com/bug?extid=4af46ee83100e99bce09
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

patch: https://syzkaller.appspot.com/x/patch.diff?x=1105e996580000

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-...@vger.kernel.org, syzkall...@googlegroups.com.

***

Subject: [PATCH] f2fs: DEBUG: full lifecycle trace for node folio write-end-io BUG

Author: karti...@gmail.com

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

Not for upstream. Instrumentation to identify how a node folio
with mismatched folio->index and nid_of_node(folio) reaches
f2fs_write_end_io and triggers the BUG_ON reported by syzbot.

Previous test run confirmed the read-side sanity check fires
(rc=-EFSCORRUPTED) yet the same folio still reaches writeback.
This round adds traces at every cache lifecycle event so the
leak path can be pinned down:

- f2fs_finish_read_bio - async read footer check, page state
- f2fs_write_end_io - write footer check, page state
- f2fs_new_node_folio - entry, after grab, after fill_footer,
after mark_dirty
- read_node_folio - entry, with current page state
- __get_node_folio - entry and after grab, page state
- __get_node_folio - sync sanity failure on page_hit

Each trace logs folio->index, footer nid/ino, and the relevant
page flags (uptodate, dirty, writeback, refcount) so the journey
of a single NID can be reconstructed across read failure, cache
reuse, and writeback submission.

BUG_ON in f2fs_write_end_io() is intentionally retained so the

kernel halts at the failing folio and the preceding trace output

appears in the syzbot console log.

Link: https://syzkaller.appspot.com/bug?extid=4af46ee83100e99bce09
Not-Signed-off-by: Deepanshu Kartikey <karti...@gmail.com>
---

fs/f2fs/data.c | 16 +++++++++++-----
fs/f2fs/node.c | 19 ++++++++++++++++++-
2 files changed, 29 insertions(+), 6 deletions(-)

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 8d4f1e75dee3..571ba13916ef 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -174,10 +174,14 @@ static void f2fs_finish_read_bio(struct bio *bio, bool in_task)

dec_page_count(F2FS_F_SB(folio), __read_io_type(folio));

if (bio->bi_status == BLK_STS_OK &&
- F2FS_F_SB(folio)->node_inode && is_node_folio(folio) &&
- f2fs_sanity_check_node_footer(F2FS_F_SB(folio),
- folio, folio->index, NODE_TYPE_REGULAR, true))
- bio->bi_status = BLK_STS_IOERR;
+ F2FS_F_SB(folio)->node_inode && is_node_folio(folio)) {
+ int rc = f2fs_sanity_check_node_footer(F2FS_F_SB(folio),
+ folio, folio->index, NODE_TYPE_REGULAR, true);

+ pr_info("f2fs-dbg: READ end_io: index=%lu footer_nid=%u ino=%u uptodate=%d dirty=%d rc=%d\n",
+ folio->index,nid_of_node(folio),ino_of_node(folio),folio_test_uptodate(folio),folio_test_dirty(folio),rc);

+ if (rc)
+ bio->bi_status = BLK_STS_IOERR;
+ }

if (finished)
folio_end_read(folio, bio->bi_status == BLK_STS_OK);

@@ -383,8 +387,10 @@ static void f2fs_write_end_io(struct bio *bio)

}

if (is_node_folio(folio)) {
- f2fs_sanity_check_node_footer(sbi, folio,
+ int rc = f2fs_sanity_check_node_footer(sbi, folio,
folio->index, NODE_TYPE_REGULAR, true);

+ pr_info("f2fs-dbg: WRITE end_io: index=%lu footer_nid=%u ino=%u uptodate=%d dirty=%d rc=%d\n",
+ folio->index,nid_of_node(folio),ino_of_node(folio),folio_test_uptodate(folio),folio_test_dirty(folio),rc);

f2fs_bug_on(sbi, folio->index != nid_of_node(folio));
}
if (f2fs_in_warm_node_list(folio))
diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c

index 4e5bd9e4cfc3..d38b32fe7ee9 100644
--- a/fs/f2fs/node.c
+++ b/fs/f2fs/node.c
@@ -1384,6 +1384,8 @@ struct folio *f2fs_new_node_folio(struct dnode_of_data *dn, unsigned int ofs)

struct folio *folio;
int err;

+ pr_info("f2fs-dbg: NEW entry: nid=%u ino=%lu ofs=%u\n",

+ dn->nid, dn->inode->i_ino, ofs);

if (unlikely(is_inode_flag_set(dn->inode, FI_NO_ALLOC)))
return ERR_PTR(-EPERM);

@@ -1391,6 +1393,8 @@ struct folio *f2fs_new_node_folio(struct dnode_of_data *dn, unsigned int ofs)
if (IS_ERR(folio))
return folio;

+ pr_info("f2fs-dbg: NEW grabbed: nid=%u uptodate=%d dirty=%d writeback=%d refcount=%d\n",
+ dn->nid,folio_test_uptodate(folio),folio_test_dirty(folio),folio_test_writeback(folio),folio_ref_count(folio));
if (unlikely((err = inc_valid_node_count(sbi, dn->inode, !ofs))))
goto fail;

@@ -1423,10 +1427,14 @@ struct folio *f2fs_new_node_folio(struct dnode_of_data *dn, unsigned int ofs)

f2fs_folio_wait_writeback(folio, NODE, true, true);
fill_node_footer(folio, dn->nid, dn->inode->i_ino, ofs, true);
set_cold_node(folio, S_ISDIR(dn->inode->i_mode));

+ pr_info("f2fs-dbg: NEW after fill_footer: nid=%u footer_nid=%u footer_ino=%u\n",
+ dn->nid, nid_of_node(folio), ino_of_node(folio));
if (!folio_test_uptodate(folio))
folio_mark_uptodate(folio);
- if (folio_mark_dirty(folio))
+ if (folio_mark_dirty(folio)) {
+ pr_info("f2fs-dbg: NEW marked dirty: nid=%u\n", dn->nid);
dn->node_changed = true;
+ }

if (f2fs_has_xattr_block(ofs))
f2fs_i_xnid_write(dn->inode, dn->nid);
@@ -1459,6 +1467,10 @@ static int read_node_folio(struct folio *folio, blk_opf_t op_flags)
};
int err;

+ pr_info("f2fs-dbg: read_node_folio entry: index=%lu uptodate=%d dirty=%d\n",
+ folio->index,
+ folio_test_uptodate(folio),
+ folio_test_dirty(folio));
if (folio_test_uptodate(folio)) {
if (!f2fs_inode_chksum_verify(sbi, folio)) {
folio_clear_uptodate(folio);
@@ -1565,6 +1577,7 @@ static struct folio *__get_node_folio(struct f2fs_sb_info *sbi, pgoff_t nid,

struct folio *folio;
int err;

+ pr_info("f2fs-dbg: GET node_folio: nid=%lu ntype=%d\n", nid, ntype);
if (!nid)
return ERR_PTR(-ENOENT);
if (f2fs_check_nid_range(sbi, nid))

@@ -1574,6 +1587,8 @@ static struct folio *__get_node_folio(struct f2fs_sb_info *sbi, pgoff_t nid,
if (IS_ERR(folio))
return folio;

+ pr_info("f2fs-dbg: GET grabbed: nid=%lu uptodate=%d dirty=%d writeback=%d refcount=%d\n",
+ nid,folio_test_uptodate(folio),folio_test_dirty(folio),folio_test_writeback(folio),folio_ref_count(folio));
err = read_node_folio(folio, 0);
if (err < 0)
goto out_put_err;
@@ -1603,6 +1618,8 @@ static struct folio *__get_node_folio(struct f2fs_sb_info *sbi, pgoff_t nid,

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
kernel BUG in f2fs_write_end_io

f2fs-dbg: READ end_io: index=3 footer_nid=0 ino=0 uptodate=0 dirty=0 rc=-117
f2fs-dbg: READ end_io: index=3 footer_nid=0 ino=0 uptodate=0 dirty=0 rc=-117
f2fs-dbg: WRITE end_io: index=3 footer_nid=0 ino=0 uptodate=0 dirty=0 rc=-117
------------[ cut here ]------------
kernel BUG at fs/f2fs/data.c:394!

Oops: invalid opcode: 0000 [#1] SMP KASAN PTI

CPU: 1 UID: 0 PID: 42 Comm: kworker/u8:2 Not tainted syzkaller #0 PREEMPT_{RT,(full)}

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026

Workqueue: bat_events batadv_bla_periodic_work
RIP: 0010:f2fs_write_end_io+0x1a74/0x1ab0 fs/f2fs/data.c:394
Code: c6 20 3d 9b 8b e8 cc d3 f6 fc 90 0f 0b e8 54 c8 93 fd 4c 89 e7 48 c7 c6 20 3d 9b 8b e8 b5 d3 f6 fc 90 0f 0b e8 3d c8 93 fd 90 <0f> 0b e8 35 c8 93 fd 48 8b 7c 24 08 48 c7 c6 20 3d 9b 8b e8 94 d3
RSP: 0018:ffffc90000b47590 EFLAGS: 00010246
RAX: ffffffff8430e123 RBX: 0000000000001000 RCX: ffff88801f2b0000

RDX: 0000000000000100 RSI: 0000000000000000 RDI: 0000000000000100
RBP: dffffc0000000000 R08: 0000000000000000 R09: 0000000000000100

R10: dffffc0000000000 R11: fffff52000168e61 R12: ffffea0000951140
R13: 0000000000001000 R14: 0000000000000003 R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff888126274000(0000) knlGS:0000000000000000

CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: 0000000000000000 CR3: 000000002b72c000 CR4: 00000000003526f0

Call Trace:
<TASK>
blk_update_request+0x57e/0xe60 block/blk-mq.c:1016
blk_mq_end_request+0x3e/0x70 block/blk-mq.c:1178
blk_complete_reqs block/blk-mq.c:1253 [inline]
blk_done_softirq+0x10a/0x160 block/blk-mq.c:1258
handle_softirqs+0x1de/0x6d0 kernel/softirq.c:622

__do_softirq kernel/softirq.c:656 [inline]
__local_bh_enable_ip+0x170/0x2b0 kernel/softirq.c:302
local_bh_enable include/linux/bottom_half.h:33 [inline]
netif_rx+0xb9/0xf0 net/core/dev.c:5775
batadv_bla_send_claim+0xa12/0xeb0 net/batman-adv/bridge_loop_avoidance.c:447
batadv_bla_send_announce net/batman-adv/bridge_loop_avoidance.c:675 [inline]
batadv_bla_periodic_work+0x629/0xae0 net/batman-adv/bridge_loop_avoidance.c:1490
process_one_work kernel/workqueue.c:3314 [inline]
process_scheduled_works+0xb5d/0x1860 kernel/workqueue.c:3397
worker_thread+0xa53/0xfc0 kernel/workqueue.c:3478

kthread+0x388/0x470 kernel/kthread.c:436
ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---

RIP: 0010:f2fs_write_end_io+0x1a74/0x1ab0 fs/f2fs/data.c:394
Code: c6 20 3d 9b 8b e8 cc d3 f6 fc 90 0f 0b e8 54 c8 93 fd 4c 89 e7 48 c7 c6 20 3d 9b 8b e8 b5 d3 f6 fc 90 0f 0b e8 3d c8 93 fd 90 <0f> 0b e8 35 c8 93 fd 48 8b 7c 24 08 48 c7 c6 20 3d 9b 8b e8 94 d3
RSP: 0018:ffffc90000b47590 EFLAGS: 00010246
RAX: ffffffff8430e123 RBX: 0000000000001000 RCX: ffff88801f2b0000

RDX: 0000000000000100 RSI: 0000000000000000 RDI: 0000000000000100
RBP: dffffc0000000000 R08: 0000000000000000 R09: 0000000000000100

R10: dffffc0000000000 R11: fffff52000168e61 R12: ffffea0000951140
R13: 0000000000001000 R14: 0000000000000003 R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff888126274000(0000) knlGS:0000000000000000

CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: 0000000000000000 CR3: 000000002b72c000 CR4: 00000000003526f0

Tested on:

commit: 66182ca8 Merge tag 'net-7.1-rc4' of git://git.kernel.o..
git tree: upstream

console output: https://syzkaller.appspot.com/x/log.txt?x=142d20ec580000

kernel config: https://syzkaller.appspot.com/x/.config?x=f2e8ebfec4636d32
dashboard link: https://syzkaller.appspot.com/bug?extid=4af46ee83100e99bce09
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

patch: https://syzkaller.appspot.com/x/patch.diff?x=1400d636580000

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-...@vger.kernel.org, syzkall...@googlegroups.com.

***

Subject: [PATCH] f2fs: don't BUG on node footer mismatch in f2fs_write_end_io

Author: karti...@gmail.com

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

Syzbot reports a recurrence of the kernel BUG in f2fs_write_end_io:

kernel BUG at fs/f2fs/data.c:388!
Oops: invalid opcode: 0000 [#1] SMP KASAN PTI

CPU: 0 UID: 0 PID: 15 Comm: ksoftirqd/0 PREEMPT_{RT,(full)}
RIP: 0010:f2fs_write_end_io+0x16df/0x1740
Call Trace:
blk_update_request+0x57e/0xe60
blk_mq_end_request+0x3e/0x70
blk_done_softirq+0x10a/0x160
handle_softirqs+0x1de/0x6d0
run_ksoftirqd+0x52/0x180

Commit 50ac3ecd8e05 ("f2fs: fix to do sanity check on node footer
in {read,write}_end_io") added f2fs_sanity_check_node_footer() to
both end_io paths to catch corrupted node footers reachable from
fuzzed on-disk images. In f2fs_write_end_io(), however, the
existing

f2fs_bug_on(sbi, folio->index != nid_of_node(folio));

was left in place immediately after the new helper call. The
helper detects the mismatch, sets SBI_NEED_FSCK and emits a
ratelimited warning, but its return value is discarded and the
following f2fs_bug_on() panics on the exact same condition.

Tracing the reproducer confirms the failure path. A node folio
with index=11 is looked up via __get_node_folio(), the
synchronous sanity check at page_hit fails with -EFSCORRUPTED
and out_err clears uptodate but leaves the dirty bit set from
the folio's earlier lifecycle. A subsequent read_node_folio()
fails with the same error (footer_nid=0, ino=0), and
folio_end_read(folio, false) does not clear dirty either. The
writeback iterator then finds the still-dirty folio via the
PAGECACHE_TAG_DIRTY tag and submits it. f2fs_write_end_io()
observes folio->index=11 with nid_of_node(folio)=0 and panics
from softirq context via blk_done_softirq, even though
f2fs_sanity_check_node_footer() has already correctly identified
the corruption and would have signalled it via its return value.

A filesystem inconsistency reachable from a mounted image must
not panic the kernel. Mirror the handling already used in
f2fs_finish_read_bio(): capture the helper's return value and
mark the bio with BLK_STS_IOERR on mismatch instead of issuing
BUG_ON. SBI_NEED_FSCK is set by the helper, so fsck.f2fs will
repair the inconsistency on the next mount.

Reported-by: syzbot+4af46e...@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=4af46ee83100e99bce09
Fixes: 50ac3ecd8e05 ("f2fs: fix to do sanity check on node footer in {read,write}_end_io")

Signed-off-by: Deepanshu Kartikey <karti...@gmail.com>
---

fs/f2fs/data.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 8d4f1e75dee3..c149b0ccf22d 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -382,11 +382,11 @@ static void f2fs_write_end_io(struct bio *bio)
STOP_CP_REASON_WRITE_FAIL);
}

- if (is_node_folio(folio)) {
- f2fs_sanity_check_node_footer(sbi, folio,
- folio->index, NODE_TYPE_REGULAR, true);
- f2fs_bug_on(sbi, folio->index != nid_of_node(folio));
- }
+ if (is_node_folio(folio) &&
+ f2fs_sanity_check_node_footer(sbi, folio,
+ folio->index, NODE_TYPE_REGULAR, true))

+ bio->bi_status = BLK_STS_IOERR;
+

if (f2fs_in_warm_node_list(folio))
f2fs_del_fsync_node_entry(sbi, folio);

--
2.43.0

[syzbot]

Hello,

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

Reported-by: syzbot+4af46e...@syzkaller.appspotmail.com
Tested-by: syzbot+4af46e...@syzkaller.appspotmail.com

Tested on:

commit: 66182ca8 Merge tag 'net-7.1-rc4' of git://git.kernel.o..
git tree: upstream

console output: https://syzkaller.appspot.com/x/log.txt?x=16a0f0c8580000

kernel config: https://syzkaller.appspot.com/x/.config?x=f2e8ebfec4636d32
dashboard link: https://syzkaller.appspot.com/bug?extid=4af46ee83100e99bce09
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

patch: https://syzkaller.appspot.com/x/patch.diff?x=16d3df6c580000

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