[syzbot] [exfat?] general protection fault in exfat_utf16_to_nls

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: b5a4da2c459f Add linux-next specific files for 20250924
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=15ffad34580000
kernel config: https://syzkaller.appspot.com/x/.config?x=fc64d939cce41d2
dashboard link: https://syzkaller.appspot.com/bug?extid=3e9cb93e3c5f90d28e19
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1704cf12580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=15c8d4e2580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/127c931e6696/disk-b5a4da2c.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/cf4957abd39e/vmlinux-b5a4da2c.xz
kernel image: https://storage.googleapis.com/syzbot-assets/860d3ac61bac/bzImage-b5a4da2c.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/9006b1673f9f/mount_0.gz
fsck result: failed (log: https://syzkaller.appspot.com/x/fsck.log?x=11c8d4e2580000)

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+3e9cb9...@syzkaller.appspotmail.com

Oops: general protection fault, probably for non-canonical address 0xdffffc0000000002: 0000 [#1] SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000010-0x0000000000000017]
CPU: 1 UID: 0 PID: 5979 Comm: syz-executor Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
RIP: 0010:exfat_convert_ucs2_to_char fs/exfat/nls.c:441 [inline]
RIP: 0010:__exfat_utf16_to_nls fs/exfat/nls.c:554 [inline]
RIP: 0010:exfat_utf16_to_nls+0x21c/0x840 fs/exfat/nls.c:638
Code: 2e 29 ff 66 41 83 fc 7f 77 14 e8 7f 2a 29 ff e9 b6 00 00 00 e8 75 2a 29 ff e9 a9 00 00 00 48 8b 4c 24 40 48 89 c8 48 c1 e8 03 <42> 80 3c 38 00 74 0f 48 8b 7c 24 40 e8 d3 6b 8e ff 48 8b 4c 24 40
RSP: 0018:ffffc90003fef760 EFLAGS: 00010202
RAX: 0000000000000002 RBX: 0000000000000004 RCX: 0000000000000010
RDX: ffff88802f18bc80 RSI: 00000000000000e1 RDI: 0000000000000080
RBP: ffffc90003fef850 R08: 0000000000000005 R09: 0000000000000000
R10: ffffc90003fef7e0 R11: fffff520007fdefc R12: 00000000000000e1
R13: ffffc90003fefa48 R14: 0000000000000000 R15: dffffc0000000000
FS: 000055557b9c2500(0000) GS:ffff888125b03000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055557b9e5608 CR3: 00000000734c8000 CR4: 00000000003526f0
Call Trace:
<TASK>
exfat_readdir fs/exfat/dir.c:143 [inline]
exfat_iterate+0x19a7/0x2050 fs/exfat/dir.c:243
wrap_directory_iterator+0x96/0xe0 fs/readdir.c:65
iterate_dir+0x399/0x570 fs/readdir.c:108
__do_sys_getdents64 fs/readdir.c:410 [inline]
__se_sys_getdents64+0xe4/0x260 fs/readdir.c:396
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f2c837c1833
Code: c1 66 0f 1f 44 00 00 48 83 c4 08 48 89 ef 5b 5d e9 32 3d f8 ff 66 90 b8 ff ff ff 7f 48 39 c2 48 0f 47 d0 b8 d9 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 05 c3 0f 1f 40 00 48 c7 c2 a8 ff ff ff f7 d8
RSP: 002b:00007ffc8cf73ff8 EFLAGS: 00000293 ORIG_RAX: 00000000000000d9
RAX: ffffffffffffffda RBX: 000055557b9dd600 RCX: 00007f2c837c1833
RDX: 0000000000008000 RSI: 000055557b9dd600 RDI: 0000000000000005
RBP: 000055557b9dd5d4 R08: 0000000000028a41 R09: 0000000000000000
R10: 00007f2c839b7cc0 R11: 0000000000000293 R12: ffffffffffffffa8
R13: 0000000000000010 R14: 000055557b9dd5d0 R15: 00007ffc8cf762b0
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:exfat_convert_ucs2_to_char fs/exfat/nls.c:441 [inline]
RIP: 0010:__exfat_utf16_to_nls fs/exfat/nls.c:554 [inline]
RIP: 0010:exfat_utf16_to_nls+0x21c/0x840 fs/exfat/nls.c:638
Code: 2e 29 ff 66 41 83 fc 7f 77 14 e8 7f 2a 29 ff e9 b6 00 00 00 e8 75 2a 29 ff e9 a9 00 00 00 48 8b 4c 24 40 48 89 c8 48 c1 e8 03 <42> 80 3c 38 00 74 0f 48 8b 7c 24 40 e8 d3 6b 8e ff 48 8b 4c 24 40
RSP: 0018:ffffc90003fef760 EFLAGS: 00010202
RAX: 0000000000000002 RBX: 0000000000000004 RCX: 0000000000000010
RDX: ffff88802f18bc80 RSI: 00000000000000e1 RDI: 0000000000000080
RBP: ffffc90003fef850 R08: 0000000000000005 R09: 0000000000000000
R10: ffffc90003fef7e0 R11: fffff520007fdefc R12: 00000000000000e1
R13: ffffc90003fefa48 R14: 0000000000000000 R15: dffffc0000000000
FS: 000055557b9c2500(0000) GS:ffff888125a03000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000c000692800 CR3: 00000000734c8000 CR4: 00000000003526f0
----------------
Code disassembly (best guess):
0: 2e 29 ff cs sub %edi,%edi
3: 66 41 83 fc 7f cmp $0x7f,%r12w
8: 77 14 ja 0x1e
a: e8 7f 2a 29 ff call 0xff292a8e
f: e9 b6 00 00 00 jmp 0xca
14: e8 75 2a 29 ff call 0xff292a8e
19: e9 a9 00 00 00 jmp 0xc7
1e: 48 8b 4c 24 40 mov 0x40(%rsp),%rcx
23: 48 89 c8 mov %rcx,%rax
26: 48 c1 e8 03 shr $0x3,%rax
* 2a: 42 80 3c 38 00 cmpb $0x0,(%rax,%r15,1) <-- trapping instruction
2f: 74 0f je 0x40
31: 48 8b 7c 24 40 mov 0x40(%rsp),%rdi
36: e8 d3 6b 8e ff call 0xff8e6c0e
3b: 48 8b 4c 24 40 mov 0x40(%rsp),%rcx


---
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:
#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

[syzbot]

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

***

Subject: Re: [syzbot] [exfat?] general protection fault in exfat_utf16_to_nls
Author: ekffu...@gmail.com

#syz test

diff --git a/fs/exfat/super.c b/fs/exfat/super.c
index e1cffa46eb73..0e3f33a26005 100644
--- a/fs/exfat/super.c
+++ b/fs/exfat/super.c
@@ -757,6 +757,11 @@ static int exfat_reconfigure(struct fs_context *fc)
if (new_opts->allow_utime == (unsigned short)-1)
new_opts->allow_utime = ~new_opts->fs_dmask & 0022;

+ if (!strcmp(new_opts->iocharset, "utf8"))
+ new_opts->utf8 = 1;
+ else
+ new_opts->utf8 = 0;
+
/*
* Since the old settings of these mount options are cached in
* inodes or dentries, they cannot be modified dynamically.

> --
> You received this message because you are subscribed to the Google Groups "syzkaller-bugs" group.
> To unsubscribe from this group and stop receiving emails from it, send an email to syzkaller-bug...@googlegroups.com.
> To view this discussion visit https://groups.google.com/d/msgid/syzkaller-bugs/68d46aed.050a0220.57ae1.0002.GAE%40google.com.

[syzbot]

Hello,

syzbot tried to test the proposed patch but the build/boot failed:

failed to apply patch:
checking file fs/exfat/super.c
patch: **** unexpected end of file in patch



Tested on:

commit: b5a4da2c Add linux-next specific files for 20250924
git tree: linux-next

kernel config: https://syzkaller.appspot.com/x/.config?x=fc64d939cce41d2
dashboard link: https://syzkaller.appspot.com/bug?extid=3e9cb93e3c5f90d28e19
compiler:

patch: https://syzkaller.appspot.com/x/patch.diff?x=106bd4e2580000

[syzbot]

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

***

Subject: Re: [syzbot] [exfat?] general protection fault in exfat_utf16_to_nls
Author: ekffu...@gmail.com

#syz test

diff --git a/fs/exfat/super.c b/fs/exfat/super.c
index e1cffa46eb73..0e3f33a26005 100644
--- a/fs/exfat/super.c
+++ b/fs/exfat/super.c
@@ -757,6 +757,11 @@ static int exfat_reconfigure(struct fs_context *fc)
if (new_opts->allow_utime == (unsigned short)-1)
new_opts->allow_utime = ~new_opts->fs_dmask & 0022;

+ if (!strcmp(new_opts->iocharset, "utf8"))
+ new_opts->utf8 = 1;
+ else
+ new_opts->utf8 = 0;
+
/*
* Since the old settings of these mount options are cached in
* inodes or dentries, they cannot be modified dynamically.

--

On Thu, Sep 25, 2025 at 7:04 AM syzbot
<syzbot+3e9cb9...@syzkaller.appspotmail.com> wrote:
>

[syzbot]

Hello,

syzbot tried to test the proposed patch but the build/boot failed:

failed to apply patch:
checking file fs/exfat/super.c
patch: **** unexpected end of file in patch



Tested on:

commit: b5a4da2c Add linux-next specific files for 20250924
git tree: linux-next

kernel config: https://syzkaller.appspot.com/x/.config?x=fc64d939cce41d2
dashboard link: https://syzkaller.appspot.com/bug?extid=3e9cb93e3c5f90d28e19
compiler:

patch: https://syzkaller.appspot.com/x/patch.diff?x=13d1e142580000

[syzbot]

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

***

Subject: Re: [syzbot] [exfat?] general protection fault in exfat_utf16_to_nls
Author: ekffu...@gmail.com

#syz test

[syzbot]

Hello,

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

Reported-by: syzbot+3e9cb9...@syzkaller.appspotmail.com
Tested-by: syzbot+3e9cb9...@syzkaller.appspotmail.com

Tested on:

commit: b5a4da2c Add linux-next specific files for 20250924
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=15ea1d34580000

kernel config: https://syzkaller.appspot.com/x/.config?x=fc64d939cce41d2
dashboard link: https://syzkaller.appspot.com/bug?extid=3e9cb93e3c5f90d28e19
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

patch: https://syzkaller.appspot.com/x/patch.diff?x=1105e142580000

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