[syzbot] [exfat?] general protection fault in exfat_init_ext_entry

[syzbot] [exfat?] general protection fault in exfat_init_ext_entry

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    f486c8aa16b8 Add linux-next specific files for 20241128
git tree:       linux-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=1549f530580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=e348a4873516af92
dashboard link: https://syzkaller.appspot.com/bug?extid=6f6c9397e0078ef60bce
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1443ef5f980000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1349f530580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/beb58ebb63cf/disk-f486c8aa.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/b241b5609e64/vmlinux-f486c8aa.xz
kernel image: https://storage.googleapis.com/syzbot-assets/c9d817f665f2/bzImage-f486c8aa.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/792711885a74/mount_0.gz

The issue was bisected to:

commit 8a3f5711ad74db9881b289a6e34d7f3b700df720
Author: Yuezhang Mo <Yuezhang.Mo@sony.com>
Date:   Thu Sep 12 08:57:06 2024 +0000

    exfat: reduce FAT chain traversal

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1145cf78580000
final oops:     https://syzkaller.appspot.com/x/report.txt?x=1345cf78580000
console output: https://syzkaller.appspot.com/x/log.txt?x=1545cf78580000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+6f6c9397e0078ef60bce@syzkaller.appspotmail.com
Fixes: 8a3f5711ad74 ("exfat: reduce FAT chain traversal")

syz-executor166: attempt to access beyond end of device
loop3: rw=524288, sector=167, nr_sectors = 1 limit=64
syz-executor166: attempt to access beyond end of device
loop3: rw=0, sector=161, nr_sectors = 1 limit=64
Oops: general protection fault, probably for non-canonical address 0xdffffc0000000005: 0000 [#1] PREEMPT SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000028-0x000000000000002f]
CPU: 0 UID: 0 PID: 5890 Comm: syz-executor166 Not tainted 6.12.0-next-20241128-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
RIP: 0010:exfat_get_dentry_cached fs/exfat/dir.c:727 [inline]
RIP: 0010:exfat_init_ext_entry+0x3fd/0x990 fs/exfat/dir.c:498
Code: 48 98 49 8d 1c c6 48 89 d8 48 c1 e8 03 42 80 3c 38 00 74 08 48 89 df e8 01 26 89 ff 48 8b 1b 48 83 c3 28 48 89 d8 48 c1 e8 03 <42> 80 3c 38 00 74 08 48 89 df e8 e4 25 89 ff 4c 8b 33 43 80 7c 3d
RSP: 0018:ffffc900041ff318 EFLAGS: 00010206
RAX: 0000000000000005 RBX: 0000000000000028 RCX: 0000000000000009
RDX: 0000000000000000 RSI: 0000000000000009 RDI: 0000000000000020
RBP: 0000000000000200 R08: ffffffff8281406f R09: 0000000000000002
R10: ffff88805d092022 R11: ffffed100ba12407 R12: ffffc900041ff700
R13: 1ffff9200083fee0 R14: ffffc900041ff710 R15: dffffc0000000000
FS:  00007fb6d86536c0(0000) GS:ffff8880b8600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fb6d8653d58 CR3: 000000002fc0c000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 exfat_add_entry+0x529/0xaa0 fs/exfat/namei.c:517
 exfat_create+0x1c7/0x570 fs/exfat/namei.c:565
 lookup_open fs/namei.c:3649 [inline]
 open_last_lookups fs/namei.c:3748 [inline]
 path_openat+0x1c03/0x3590 fs/namei.c:3984
 do_filp_open+0x27f/0x4e0 fs/namei.c:4014
 do_sys_openat2+0x13e/0x1d0 fs/open.c:1402
 do_sys_open fs/open.c:1417 [inline]
 __do_sys_creat fs/open.c:1495 [inline]
 __se_sys_creat fs/open.c:1489 [inline]
 __x64_sys_creat+0x123/0x170 fs/open.c:1489
 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
RIP: 0033:0x7fb6d86c4099
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 01 1b 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:00007fb6d8653218 EFLAGS: 00000246 ORIG_RAX: 0000000000000055
RAX: ffffffffffffffda RBX: 00007fb6d87534b8 RCX: 00007fb6d86c4099
RDX: 00007fb6d869bc26 RSI: 0000000000000000 RDI: 0000000020000e00
RBP: 00007fb6d87534b0 R08: 00007ffed34fd087 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007fb6d8718d84
R13: 00007fb6d8717880 R14: 0032656c69662f2e R15: 6f6f6c2f7665642f
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:exfat_get_dentry_cached fs/exfat/dir.c:727 [inline]
RIP: 0010:exfat_init_ext_entry+0x3fd/0x990 fs/exfat/dir.c:498
Code: 48 98 49 8d 1c c6 48 89 d8 48 c1 e8 03 42 80 3c 38 00 74 08 48 89 df e8 01 26 89 ff 48 8b 1b 48 83 c3 28 48 89 d8 48 c1 e8 03 <42> 80 3c 38 00 74 08 48 89 df e8 e4 25 89 ff 4c 8b 33 43 80 7c 3d
RSP: 0018:ffffc900041ff318 EFLAGS: 00010206
RAX: 0000000000000005 RBX: 0000000000000028 RCX: 0000000000000009
RDX: 0000000000000000 RSI: 0000000000000009 RDI: 0000000000000020
RBP: 0000000000000200 R08: ffffffff8281406f R09: 0000000000000002
R10: ffff88805d092022 R11: ffffed100ba12407 R12: ffffc900041ff700
R13: 1ffff9200083fee0 R14: ffffc900041ff710 R15: dffffc0000000000
FS:  00007fb6d86536c0(0000) GS:ffff8880b8700000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055bc85806ca8 CR3: 000000002fc0c000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess):
   0:	48 98                	cltq
   2:	49 8d 1c c6          	lea    (%r14,%rax,8),%rbx
   6:	48 89 d8             	mov    %rbx,%rax
   9:	48 c1 e8 03          	shr    $0x3,%rax
   d:	42 80 3c 38 00       	cmpb   $0x0,(%rax,%r15,1)
  12:	74 08                	je     0x1c
  14:	48 89 df             	mov    %rbx,%rdi
  17:	e8 01 26 89 ff       	call   0xff89261d
  1c:	48 8b 1b             	mov    (%rbx),%rbx
  1f:	48 83 c3 28          	add    $0x28,%rbx
  23:	48 89 d8             	mov    %rbx,%rax
  26:	48 c1 e8 03          	shr    $0x3,%rax
* 2a:	42 80 3c 38 00       	cmpb   $0x0,(%rax,%r15,1) <-- trapping instruction
  2f:	74 08                	je     0x39
  31:	48 89 df             	mov    %rbx,%rdi
  34:	e8 e4 25 89 ff       	call   0xff89261d
  39:	4c 8b 33             	mov    (%rbx),%r14
  3c:	43                   	rex.XB
  3d:	80                   	.byte 0x80
  3e:	7c 3d                	jl     0x7d


---
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] [exfat?] general protection fault in exfat_init_ext_entry

[Yuezhang.Mo]

[-- Attachment #1: Type: text/plain, Size: 9 bytes --]

#syz test

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #2: v1-0001-exfat-fix-error-handling-for-exfat_find_empty_ent.patch --]
[-- Type: text/x-patch; name="v1-0001-exfat-fix-error-handling-for-exfat_find_empty_ent.patch", Size: 769 bytes --]

From c67f805c214c0be424ab37bed889746b9105472a Mon Sep 17 00:00:00 2001
From: Yuezhang Mo <Yuezhang.Mo@sony.com>
Date: Mon, 2 Dec 2024 09:53:17 +0800
Subject: [PATCH v1] exfat: fix error handling for exfat_find_empty_entry()

Signed-off-by: Yuezhang Mo <Yuezhang.Mo@sony.com>
---
 fs/exfat/namei.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/exfat/namei.c b/fs/exfat/namei.c
index ca616f2f2c8a..41d5090b237b 100644
--- a/fs/exfat/namei.c
+++ b/fs/exfat/namei.c
@@ -395,6 +395,9 @@ static int exfat_find_empty_entry(struct inode *inode,
 		inode->i_blocks += sbi->cluster_size >> 9;
 	}
 
+	if (dentry < 0)
+		return dentry;
+
 	p_dir->dir = exfat_sector_to_cluster(sbi, es->bh[0]->b_blocknr);
 	p_dir->size -= dentry / sbi->dentries_per_clu;
 
-- 
2.43.0

Re: [syzbot] [exfat?] general protection fault in exfat_init_ext_entry

[syzbot]

Hello,

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

Reported-by: syzbot+6f6c9397e0078ef60bce@syzkaller.appspotmail.com
Tested-by: syzbot+6f6c9397e0078ef60bce@syzkaller.appspotmail.com

Tested on:

commit:         f486c8aa Add linux-next specific files for 20241128
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=159ae7c0580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=e348a4873516af92
dashboard link: https://syzkaller.appspot.com/bug?extid=6f6c9397e0078ef60bce
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=1068bd30580000

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

Re: [syzbot] [exfat?] general protection fault in exfat_init_ext_entry

[Yuezhang.Mo]

[-- Attachment #1: Type: text/plain, Size: 9 bytes --]

#syz test

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #2: 0001-exfat-fix-exfat_find_empty_entry-not-returning-error.patch --]
[-- Type: text/x-patch; name="0001-exfat-fix-exfat_find_empty_entry-not-returning-error.patch", Size: 828 bytes --]

From 9bedc4c5a1d5d7b6b816eb5f956f5ab0db5eba36 Mon Sep 17 00:00:00 2001
From: Yuezhang Mo <Yuezhang.Mo@sony.com>
Date: Mon, 2 Dec 2024 09:53:17 +0800
Subject: [PATCH] exfat: fix exfat_find_empty_entry() not returning error on
 failure

Signed-off-by: Yuezhang Mo <Yuezhang.Mo@sony.com>
---
 fs/exfat/namei.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/exfat/namei.c b/fs/exfat/namei.c
index f203c53277e2..c24b62681535 100644
--- a/fs/exfat/namei.c
+++ b/fs/exfat/namei.c
@@ -330,8 +330,8 @@ static int exfat_find_empty_entry(struct inode *inode,
 
 	while ((dentry = exfat_search_empty_slot(sb, &hint_femp, p_dir,
 					num_entries, es)) < 0) {
-		if (dentry == -EIO)
-			break;
+		if (dentry != -ENOSPC)
+			return dentry;
 
 		if (exfat_check_max_dentries(inode))
 			return -ENOSPC;
-- 
2.43.0

Re: [syzbot] [exfat?] general protection fault in exfat_init_ext_entry

[syzbot]

Hello,

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

Reported-by: syzbot+6f6c9397e0078ef60bce@syzkaller.appspotmail.com
Tested-by: syzbot+6f6c9397e0078ef60bce@syzkaller.appspotmail.com

Tested on:

commit:         f486c8aa Add linux-next specific files for 20241128
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=14eab0df980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=e348a4873516af92
dashboard link: https://syzkaller.appspot.com/bug?extid=6f6c9397e0078ef60bce
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=17e30330580000

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