[syzbot] [fs?] general protection fault in iter_file_splice_write

[syzbot] [fs?] general protection fault in iter_file_splice_write

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    33e02dc69afb Merge tag 'sound-6.10-rc1' of git://git.kerne..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13ad18d0980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=25544a2faf4bae65
dashboard link: https://syzkaller.appspot.com/bug?extid=d2125fcb6aa8c4276fd2
compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1526a8dc980000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=14f53ae4980000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7bc7510fe41f/non_bootable_disk-33e02dc6.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/573c88ac3233/vmlinux-33e02dc6.xz
kernel image: https://storage.googleapis.com/syzbot-assets/760a52b9a00a/bzImage-33e02dc6.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+d2125fcb6aa8c4276fd2@syzkaller.appspotmail.com

Oops: general protection fault, probably for non-canonical address 0xdffffc0000000001: 0000 [#1] PREEMPT SMP KASAN NOPTI
KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
CPU: 3 PID: 5196 Comm: syz-executor259 Not tainted 6.9.0-syzkaller-07370-g33e02dc69afb #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
RIP: 0010:pipe_buf_release include/linux/pipe_fs_i.h:219 [inline]
RIP: 0010:iter_file_splice_write+0xa24/0x10b0 fs/splice.c:759
Code: 00 48 89 fa 48 c1 ea 03 80 3c 1a 00 0f 85 b1 04 00 00 4d 8b 65 10 49 c7 45 10 00 00 00 00 49 8d 7c 24 08 48 89 fa 48 c1 ea 03 <80> 3c 1a 00 0f 85 1a 05 00 00 49 8b 54 24 08 4c 89 ee 4c 89 ff 83
RSP: 0018:ffffc900031b7930 EFLAGS: 00010202
RAX: 0000000000000000 RBX: dffffc0000000000 RCX: ffffffff8209a1a8
RDX: 0000000000000001 RSI: ffffffff8209a06c RDI: 0000000000000008
RBP: 000000000000003d R08: 0000000000000006 R09: 0000000000000000
R10: 7fffffffffffefff R11: 0000000000000001 R12: 0000000000000000
R13: ffff888026d5a208 R14: 7fffffffffffefff R15: ffff88801e5c5800
FS:  00007f78cdfc16c0(0000) GS:ffff88806b300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f78ce0454d0 CR3: 0000000019dc8000 CR4: 0000000000350ef0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 do_splice_from fs/splice.c:941 [inline]
 direct_splice_actor+0x19b/0x6d0 fs/splice.c:1164
 splice_direct_to_actor+0x346/0xa40 fs/splice.c:1108
 do_splice_direct_actor fs/splice.c:1207 [inline]
 do_splice_direct+0x17e/0x250 fs/splice.c:1233
 do_sendfile+0xaa8/0xdb0 fs/read_write.c:1295
 __do_sys_sendfile64 fs/read_write.c:1362 [inline]
 __se_sys_sendfile64 fs/read_write.c:1348 [inline]
 __x64_sys_sendfile64+0x1da/0x220 fs/read_write.c:1348
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcf/0x260 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f78ce009d09
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 81 18 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f78cdfc1168 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 00007f78ce091328 RCX: 00007f78ce009d09
RDX: 0000000000000000 RSI: 0000000000000004 RDI: 0000000000000004
RBP: 00007f78ce091320 R08: 00007f78cdfc16c0 R09: 0000000000000000
R10: 0000000100000000 R11: 0000000000000246 R12: 00007f78ce09132c
R13: 0000000000000006 R14: 00007ffe98369ff0 R15: 00007ffe9836a0d8
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:pipe_buf_release include/linux/pipe_fs_i.h:219 [inline]
RIP: 0010:iter_file_splice_write+0xa24/0x10b0 fs/splice.c:759
Code: 00 48 89 fa 48 c1 ea 03 80 3c 1a 00 0f 85 b1 04 00 00 4d 8b 65 10 49 c7 45 10 00 00 00 00 49 8d 7c 24 08 48 89 fa 48 c1 ea 03 <80> 3c 1a 00 0f 85 1a 05 00 00 49 8b 54 24 08 4c 89 ee 4c 89 ff 83
RSP: 0018:ffffc900031b7930 EFLAGS: 00010202
RAX: 0000000000000000 RBX: dffffc0000000000 RCX: ffffffff8209a1a8
RDX: 0000000000000001 RSI: ffffffff8209a06c RDI: 0000000000000008
RBP: 000000000000003d R08: 0000000000000006 R09: 0000000000000000
R10: 7fffffffffffefff R11: 0000000000000001 R12: 0000000000000000
R13: ffff888026d5a208 R14: 7fffffffffffefff R15: ffff88801e5c5800
FS:  00007f78cdfc16c0(0000) GS:ffff88806b200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f78ce05d0d8 CR3: 0000000019dc8000 CR4: 0000000000350ef0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess):
   0:	00 48 89             	add    %cl,-0x77(%rax)
   3:	fa                   	cli
   4:	48 c1 ea 03          	shr    $0x3,%rdx
   8:	80 3c 1a 00          	cmpb   $0x0,(%rdx,%rbx,1)
   c:	0f 85 b1 04 00 00    	jne    0x4c3
  12:	4d 8b 65 10          	mov    0x10(%r13),%r12
  16:	49 c7 45 10 00 00 00 	movq   $0x0,0x10(%r13)
  1d:	00
  1e:	49 8d 7c 24 08       	lea    0x8(%r12),%rdi
  23:	48 89 fa             	mov    %rdi,%rdx
  26:	48 c1 ea 03          	shr    $0x3,%rdx
* 2a:	80 3c 1a 00          	cmpb   $0x0,(%rdx,%rbx,1) <-- trapping instruction
  2e:	0f 85 1a 05 00 00    	jne    0x54e
  34:	49 8b 54 24 08       	mov    0x8(%r12),%rdx
  39:	4c 89 ee             	mov    %r13,%rsi
  3c:	4c 89 ff             	mov    %r15,%rdi
  3f:	83                   	.byte 0x83


---
This report is generated by a bot. It may contain errors.
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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
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#syz undup

[PATCH] netfs: if extracting pages from user iterator fails return 0

[Lizhi Xu]

When extracting the pages from a user iterator fails, netfs_extract_user_iter()
will return 0, this situation will result in an abnormal and oversized return 
value for netfs_unbuffered_writer_locked() (for example, 9223372036854775807).

Therefore, when the number of extracted pages is 0, set ret to 0 and jump to out.

Reported-and-tested-by: syzbot+d2125fcb6aa8c4276fd2@syzkaller.appspotmail.com
Signed-off-by: Lizhi Xu <lizhi.xu@windriver.com>
---
 fs/netfs/direct_write.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/netfs/direct_write.c b/fs/netfs/direct_write.c
index 608ba6416919..d74761fb1876 100644
--- a/fs/netfs/direct_write.c
+++ b/fs/netfs/direct_write.c
@@ -69,7 +69,7 @@ static ssize_t netfs_unbuffered_write_iter_locked(struct kiocb *iocb, struct iov
 		 */
 		if (async || user_backed_iter(iter)) {
 			n = netfs_extract_user_iter(iter, len, &wreq->iter, 0);
-			if (n < 0) {
+			if (n <= 0) {
 				ret = n;
 				goto out;
 			}
-- 
2.43.0

Re: [syzbot] [fs?] general protection fault in iter_file_splice_write

[syzbot]

syzbot has bisected this issue to:

commit 2df86547b23dabcd02ab000a24ed7813606c269f
Author: David Howells <dhowells@redhat.com>
Date:   Fri Mar 8 12:36:05 2024 +0000

    netfs: Cut over to using new writeback code

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=148b014b980000
start commit:   5189dafa4cf9 Merge tag 'nfsd-6.11-1' of git://git.kernel.o..
git tree:       upstream
final oops:     https://syzkaller.appspot.com/x/report.txt?x=168b014b980000
console output: https://syzkaller.appspot.com/x/log.txt?x=128b014b980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=e8a2eef9745ade09
dashboard link: https://syzkaller.appspot.com/bug?extid=d2125fcb6aa8c4276fd2
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=16828c5d980000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=103c7805980000

Reported-by: syzbot+d2125fcb6aa8c4276fd2@syzkaller.appspotmail.com
Fixes: 2df86547b23d ("netfs: Cut over to using new writeback code")

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

Re: [syzbot] [fs?] general protection fault in iter_file_splice_write

[syzbot]

syzbot suspects this issue was fixed by commit:

commit a3de58b12ce074ec05b8741fa28d62ccb1070468
Author: David Howells <dhowells@redhat.com>
Date:   Thu Aug 14 21:45:50 2025 +0000

    netfs: Fix unbuffered write error handling

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=162dc142580000
start commit:   5189dafa4cf9 Merge tag 'nfsd-6.11-1' of git://git.kernel.o..
git tree:       upstream
kernel config:  https://syzkaller.appspot.com/x/.config?x=e8a2eef9745ade09
dashboard link: https://syzkaller.appspot.com/bug?extid=d2125fcb6aa8c4276fd2
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=16828c5d980000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=103c7805980000

If the result looks correct, please mark the issue as fixed by replying with:

#syz fix: netfs: Fix unbuffered write error handling

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

Re: [syzbot] [fs?] general protection fault in iter_file_splice_write

[David Howells]

#syz fix: netfs: Fix unbuffered write error handling