[syzbot] [block?] general protection fault in bio_first_folio

[syzbot] [block?] general protection fault in bio_first_folio

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    abb240f7a2bd Add linux-next specific files for 20231212
git tree:       linux-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=1673c8aee80000
kernel config:  https://syzkaller.appspot.com/x/.config?x=cc2485c21b49ddc4
dashboard link: https://syzkaller.appspot.com/bug?extid=8b23309d5788a79d3eea
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=11627092e80000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13274512e80000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/795a3560ea0e/disk-abb240f7.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/17a88d6802ed/vmlinux-abb240f7.xz
kernel image: https://storage.googleapis.com/syzbot-assets/bfcdd0049f21/bzImage-abb240f7.xz

The issue was bisected to:

commit 1b151e2435fc3a9b10c8946c6aebe9f3e1938c55
Author: Matthew Wilcox (Oracle) <willy@infradead.org>
Date:   Mon Aug 14 14:41:00 2023 +0000

    block: Remove special-casing of compound pages

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=152f8a8ee80000
final oops:     https://syzkaller.appspot.com/x/report.txt?x=172f8a8ee80000
console output: https://syzkaller.appspot.com/x/log.txt?x=132f8a8ee80000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+8b23309d5788a79d3eea@syzkaller.appspotmail.com
Fixes: 1b151e2435fc ("block: Remove special-casing of compound pages")

general protection fault, probably for non-canonical address 0xdffffc0000000001: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
CPU: 0 PID: 5059 Comm: syz-executor696 Not tainted 6.7.0-rc5-next-20231212-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/10/2023
RIP: 0010:_compound_head include/linux/page-flags.h:247 [inline]
RIP: 0010:bio_first_folio+0xcb/0x5c0 include/linux/bio.h:289
Code: 48 89 ea 48 c1 ea 03 80 3c 02 00 0f 85 76 04 00 00 48 b8 00 00 00 00 00 fc ff df 4c 8b 6d 00 49 8d 7d 08 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 49 04 00 00 4d 8b 7d 08 31 ff 4d 89 fc 41 83 e4
RSP: 0018:ffffc900039ef448 EFLAGS: 00010202
RAX: dffffc0000000000 RBX: ffffc900039ef4e8 RCX: ffffffff8444f4bd
RDX: 0000000000000001 RSI: ffffffff8444f4cb RDI: 0000000000000008
RBP: ffff88801dad0888 R08: 0000000000000003 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000001 R12: ffff88801dad0800
R13: 0000000000000000 R14: 0000000000000000 R15: ffff88801dad0800
FS:  0000555556ace380(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000005fdeb8 CR3: 000000007c5b7000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 __bio_release_pages+0x9d/0x4b0 block/bio.c:1150
 bio_release_pages include/linux/bio.h:508 [inline]
 bio_map_user_iov+0x8ee/0xa60 block/blk-map.c:347
 blk_rq_map_user_iov+0x6a5/0x1840 block/blk-map.c:663
 blk_rq_map_user block/blk-map.c:690 [inline]
 blk_rq_map_user_io+0x202/0x230 block/blk-map.c:723
 sg_io+0x537/0xd70 drivers/scsi/scsi_ioctl.c:456
 scsi_cdrom_send_packet+0x276/0x640 drivers/scsi/scsi_ioctl.c:820
 scsi_ioctl+0x146/0x1840 drivers/scsi/scsi_ioctl.c:903
 sg_ioctl+0xb7b/0x2760 drivers/scsi/sg.c:1163
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:871 [inline]
 __se_sys_ioctl fs/ioctl.c:857 [inline]
 __x64_sys_ioctl+0x18f/0x210 fs/ioctl.c:857
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0x40/0x110 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x62/0x6a
RIP: 0033:0x7f9970983229
Code: 48 83 c4 28 c3 e8 37 17 00 00 0f 1f 80 00 00 00 00 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 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffda6357b98 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007ffda6357d68 RCX: 00007f9970983229
RDX: 0000000020000000 RSI: 0000000000005393 RDI: 0000000000000004
RBP: 00007f99709f6610 R08: 00007ffda6357d68 R09: 00007ffda6357d68
R10: 002367732f766564 R11: 0000000000000246 R12: 0000000000000001
R13: 00007ffda6357d58 R14: 0000000000000001 R15: 0000000000000001
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:_compound_head include/linux/page-flags.h:247 [inline]
RIP: 0010:bio_first_folio+0xcb/0x5c0 include/linux/bio.h:289
Code: 48 89 ea 48 c1 ea 03 80 3c 02 00 0f 85 76 04 00 00 48 b8 00 00 00 00 00 fc ff df 4c 8b 6d 00 49 8d 7d 08 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 49 04 00 00 4d 8b 7d 08 31 ff 4d 89 fc 41 83 e4
RSP: 0018:ffffc900039ef448 EFLAGS: 00010202
RAX: dffffc0000000000 RBX: ffffc900039ef4e8 RCX: ffffffff8444f4bd
RDX: 0000000000000001 RSI: ffffffff8444f4cb RDI: 0000000000000008
RBP: ffff88801dad0888 R08: 0000000000000003 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000001 R12: ffff88801dad0800
R13: 0000000000000000 R14: 0000000000000000 R15: ffff88801dad0800
FS:  0000555556ace380(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000005fdeb8 CR3: 000000007c5b7000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess):
   0:	48 89 ea             	mov    %rbp,%rdx
   3:	48 c1 ea 03          	shr    $0x3,%rdx
   7:	80 3c 02 00          	cmpb   $0x0,(%rdx,%rax,1)
   b:	0f 85 76 04 00 00    	jne    0x487
  11:	48 b8 00 00 00 00 00 	movabs $0xdffffc0000000000,%rax
  18:	fc ff df
  1b:	4c 8b 6d 00          	mov    0x0(%rbp),%r13
  1f:	49 8d 7d 08          	lea    0x8(%r13),%rdi
  23:	48 89 fa             	mov    %rdi,%rdx
  26:	48 c1 ea 03          	shr    $0x3,%rdx
* 2a:	80 3c 02 00          	cmpb   $0x0,(%rdx,%rax,1) <-- trapping instruction
  2e:	0f 85 49 04 00 00    	jne    0x47d
  34:	4d 8b 7d 08          	mov    0x8(%r13),%r15
  38:	31 ff                	xor    %edi,%edi
  3a:	4d 89 fc             	mov    %r15,%r12
  3d:	41                   	rex.B
  3e:	83                   	.byte 0x83
  3f:	e4                   	.byte 0xe4


---
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 syzkaller@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
For information about bisection process see: https://goo.gl/tpsmEJ#bisection

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:
#syz set subsystems: new-subsystem
(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

Re: [syzbot] [block?] general protection fault in bio_first_folio

[Matthew Wilcox]

On Fri, Dec 15, 2023 at 09:20:22PM -0800, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:

Good bot.

> commit 1b151e2435fc3a9b10c8946c6aebe9f3e1938c55
> Author: Matthew Wilcox (Oracle) <willy@infradead.org>
> Date:   Mon Aug 14 14:41:00 2023 +0000
> 
>     block: Remove special-casing of compound pages
> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=152f8a8ee80000
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=172f8a8ee80000
> console output: https://syzkaller.appspot.com/x/log.txt?x=132f8a8ee80000
> 
> general protection fault, probably for non-canonical address 0xdffffc0000000001: 0000 [#1] PREEMPT SMP KASAN
> KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]

I _think_ what's happened here is that __bio_release_pages() was called
with a zero-length bio.

> CPU: 0 PID: 5059 Comm: syz-executor696 Not tainted 6.7.0-rc5-next-20231212-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/10/2023
> RIP: 0010:_compound_head include/linux/page-flags.h:247 [inline]
> RIP: 0010:bio_first_folio+0xcb/0x5c0 include/linux/bio.h:289

... bio_first_folio() doesn't handle it well, whereas
bio_for_each_segment_all() did.

> 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.

#syz test git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next abb240f7a2bd

diff --git a/include/linux/bio.h b/include/linux/bio.h
index ec4db73e5f4e..1518f1201ddd 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -286,6 +286,11 @@ static inline void bio_first_folio(struct folio_iter *fi, struct bio *bio,
 {
 	struct bio_vec *bvec = bio_first_bvec_all(bio) + i;
 
+	if (i >= bio->bi_vcnt) {
+		fi->folio = NULL;
+		return;
+	}
+
 	fi->folio = page_folio(bvec->bv_page);
 	fi->offset = bvec->bv_offset +
 			PAGE_SIZE * (bvec->bv_page - &fi->folio->page);
@@ -303,10 +308,8 @@ static inline void bio_next_folio(struct folio_iter *fi, struct bio *bio)
 		fi->offset = 0;
 		fi->length = min(folio_size(fi->folio), fi->_seg_count);
 		fi->_next = folio_next(fi->folio);
-	} else if (fi->_i + 1 < bio->bi_vcnt) {
-		bio_first_folio(fi, bio, fi->_i + 1);
 	} else {
-		fi->folio = NULL;
+		bio_first_folio(fi, bio, fi->_i + 1);
 	}
 }
 

Re: [syzbot] [block?] general protection fault in bio_first_folio

[syzbot]

Hello,

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

Reported-and-tested-by: syzbot+8b23309d5788a79d3eea@syzkaller.appspotmail.com

Tested on:

commit:         abb240f7 Add linux-next specific files for 20231212
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=13d005c6e80000
kernel config:  https://syzkaller.appspot.com/x/.config?x=cc2485c21b49ddc4
dashboard link: https://syzkaller.appspot.com/bug?extid=8b23309d5788a79d3eea
compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=12d24771e80000

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