Re: [syzbot] [block?] BUG: unable to handle kernel NULL pointer dereference in __bio_release_pages

[Jens Axboe]

On 1/16/24 11:00 AM, Jens Axboe wrote:
> On 1/16/24 2:57 AM, syzbot wrote:
>> Hello,
>>
>> syzbot found the following issue on:
>>
>> HEAD commit:    052d534373b7 Merge tag 'exfat-for-6.8-rc1' of git://git.ke..
>> git tree:       upstream
>> console output: https://syzkaller.appspot.com/x/log.txt?x=17957913e80000
>> kernel config:  https://syzkaller.appspot.com/x/.config?x=9603f9823d535d97
>> dashboard link: https://syzkaller.appspot.com/bug?extid=004c1e0fced2b4bc3dcc
>> compiler:       aarch64-linux-gnu-gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
>> userspace arch: arm64
>> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=13529733e80000
>> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=166850dde80000
>>
>> Downloadable assets:
>> disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/384ffdcca292/non_bootable_disk-052d5343.raw.xz
>> vmlinux: https://storage.googleapis.com/syzbot-assets/74cc52d4cc15/vmlinux-052d5343.xz
>> kernel image: https://storage.googleapis.com/syzbot-assets/a2da7e6a234c/Image-052d5343.gz.xz
>>
>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
>> Reported-by: syzbot+004c1e0fced2b4bc3dcc@xxxxxxxxxxxxxxxxxxxxxxxxx
>>
>> Unable to handle kernel paging request at virtual address dfff800000000001
>> KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
>> Mem abort info:
>>   ESR = 0x0000000096000005
>>   EC = 0x25: DABT (current EL), IL = 32 bits
>>   SET = 0, FnV = 0
>>   EA = 0, S1PTW = 0
>>   FSC = 0x05: level 1 translation fault
>> Data abort info:
>>   ISV = 0, ISS = 0x00000005, ISS2 = 0x00000000
>>   CM = 0, WnR = 0, TnD = 0, TagAccess = 0
>>   GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
>> [dfff800000000001] address between user and kernel address ranges
>> Internal error: Oops: 0000000096000005 [#1] PREEMPT SMP
>> Modules linked in:
>> CPU: 1 PID: 3139 Comm: syz-executor303 Not tainted 6.7.0-syzkaller-09928-g052d534373b7 #0
>> Hardware name: linux,dummy-virt (DT)
>> pstate: 10000005 (nzcV daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
>> pc : _compound_head include/linux/page-flags.h:247 [inline]
>> pc : bio_first_folio include/linux/bio.h:289 [inline]
>> pc : __bio_release_pages+0x100/0x73c block/bio.c:1153
>> lr : bio_release_pages include/linux/bio.h:508 [inline]
>> lr : blkdev_bio_end_io+0x2a0/0x3f0 block/fops.c:157
>> sp : ffff800089a375e0
>> x29: ffff800089a375e0 x28: 1fffe0000162e879 x27: ffff00000b1743c0
>> x26: ffff00000b1743c8 x25: 000000000000000a x24: 1fffe000015a9e12
>> x23: ffff00000ad4f094 x22: ffff00000f496600 x21: 1fffe0000162e87a
>> x20: 0000000000000004 x19: 0000000000000000 x18: ffff00000b174432
>> x17: ffff00000b174438 x16: ffff00000f948008 x15: 1fffe0000162e886
>> x14: ffff00000b1743d4 x13: 00000000f1f1f1f1 x12: ffff6000015a9e13
>> x11: 1fffe000015a9e12 x10: ffff6000015a9e12 x9 : dfff800000000000
>> x8 : ffff00000b1743d4 x7 : 0000000041b58ab3 x6 : 1ffff00011346ed0
>> x5 : ffff700011346ed0 x4 : 00000000f1f1f1f1 x3 : 000000000000f1f1
>> x2 : 0000000000000001 x1 : dfff800000000000 x0 : 0000000000000008
>> Call trace:
>>  _compound_head include/linux/page-flags.h:247 [inline]
>>  bio_first_folio include/linux/bio.h:289 [inline]
>>  __bio_release_pages+0x100/0x73c block/bio.c:1153
>>  bio_release_pages include/linux/bio.h:508 [inline]
>>  blkdev_bio_end_io+0x2a0/0x3f0 block/fops.c:157
>>  bio_endio+0x4a4/0x618 block/bio.c:1608
>>  __blkdev_direct_IO block/fops.c:213 [inline]
>>  blkdev_direct_IO.part.0+0xf08/0x13c0 block/fops.c:379
>>  blkdev_direct_IO block/fops.c:370 [inline]
>>  blkdev_direct_write block/fops.c:648 [inline]
>>  blkdev_write_iter+0x430/0x91c block/fops.c:706
>>  call_write_iter include/linux/fs.h:2085 [inline]
>>  do_iter_readv_writev+0x194/0x298 fs/read_write.c:741
>>  vfs_writev+0x244/0x684 fs/read_write.c:971
>>  do_pwritev+0x15c/0x1e0 fs/read_write.c:1072
>>  __do_sys_pwritev2 fs/read_write.c:1131 [inline]
>>  __se_sys_pwritev2 fs/read_write.c:1122 [inline]
>>  __arm64_sys_pwritev2+0xac/0x120 fs/read_write.c:1122
>>  __invoke_syscall arch/arm64/kernel/syscall.c:37 [inline]
>>  invoke_syscall+0x6c/0x258 arch/arm64/kernel/syscall.c:51
>>  el0_svc_common.constprop.0+0xac/0x230 arch/arm64/kernel/syscall.c:136
>>  do_el0_svc+0x40/0x58 arch/arm64/kernel/syscall.c:155
>>  el0_svc+0x58/0x140 arch/arm64/kernel/entry-common.c:678
>>  el0t_64_sync_handler+0x100/0x12c arch/arm64/kernel/entry-common.c:696
>>  el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:595
>> Code: d2d00001 f2fbffe1 91002260 d343fc02 (38e16841) 
>> ---[ end trace 0000000000000000 ]---
>> ----------------
>> Code disassembly (best guess):
>>    0:	d2d00001 	mov	x1, #0x800000000000        	// #140737488355328
>>    4:	f2fbffe1 	movk	x1, #0xdfff, lsl #48
>>    8:	91002260 	add	x0, x19, #0x8
>>    c:	d343fc02 	lsr	x2, x0, #3
>> * 10:	38e16841 	ldrsb	w1, [x2, x1] <-- trapping instruction
> 
> This looks to be caused by:
> 
> commit 1b151e2435fc3a9b10c8946c6aebe9f3e1938c55
> Author: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
> Date:   Mon Aug 14 15:41:00 2023 +0100
> 
>     block: Remove special-casing of compound pages

I suspect this should fix it.

diff --git a/block/bio.c b/block/bio.c
index b9642a41f286..d271f093abb9 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -1150,6 +1150,12 @@ void __bio_release_pages(struct bio *bio, bool mark_dirty)
 {
 	struct folio_iter fi;
 
+	/*
+	 * No pages, nothing to do
+	 */
+	if (!bio->bi_vcnt)
+		return;
+
 	bio_for_each_folio_all(fi, bio) {
 		struct page *page;
 		size_t done = 0;

-- 
Jens Axboe