[PATCH] mtd: block2mtd: Fix divide error when erase_size is zero

[PATCH] mtd: block2mtd: Fix divide error when erase_size is zero

[Pei Xiao]

The erase size is parsed from the "block2mtd" module parameter and can
be set to zero. add_device() then evaluates

	if ((long)size % erase_size)

with a zero divisor, which triggers a divide error:

	divide error: 0000 [#1] PREEMPT SMP PTI
	RIP: 0010:add_device drivers/mtd/devices/block2mtd.c:296 [inline]
	RIP: 0010:block2mtd_setup2+0x592/0xda0 drivers/mtd/devices/block2mtd.c:459
	Call Trace:
	 block2mtd_setup+0x27/0xe0 drivers/mtd/devices/block2mtd.c:476
	 param_attr_store+0x214/0x310 kernel/params.c:589
	 module_attr_store+0x65/0x90 kernel/params.c:904
	 kernfs_fop_write_iter+0x3a4/0x540 fs/kernfs/file.c:345
	 ...

Reject a zero erase size before performing the modulo operation so the
existing "erasesize must be a divisor of device size" error path
reports the invalid argument and frees the device.

Fixes: ea6d833a3fdd ("mtd: block2mtd: check device size")
Reported-by: syzbot+b320a4d5f65a61dbbf89@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/6a791c94.01d0871a.3a0d52.009b.GAE@google.com/T/#m5d4961a95b273da06457d603ddcc4170bf82a9fd
Cc: stable@vger.kernel.org
Signed-off-by: Pei Xiao <xiaopei01@kylinos.cn>
---
 drivers/mtd/devices/block2mtd.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/mtd/devices/block2mtd.c b/drivers/mtd/devices/block2mtd.c
index 03e80b2c4f5a..349fa07be314 100644
--- a/drivers/mtd/devices/block2mtd.c
+++ b/drivers/mtd/devices/block2mtd.c
@@ -293,7 +293,7 @@ static struct block2mtd_dev *add_device(char *devname, int erase_size,
 	}
 
 	size = bdev_nr_bytes(bdev);
-	if ((long)size % erase_size) {
+	if (!erase_size || (long)size % erase_size) {
 		pr_err("erasesize must be a divisor of device size\n");
 		goto err_free_block2mtd;
 	}
-- 
2.25.1

Re: [syzbot] [mtd?] divide error in block2mtd_setup2

[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit:    f5bbbfec59b4 Merge tag 'probes-fixes-v7.2-rc7' of git://gi..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13a31079580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=c44651ea7dd2f307
dashboard link: https://syzkaller.appspot.com/bug?extid=b320a4d5f65a61dbbf89
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16b76149580000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b320a4d5f65a61dbbf89@syzkaller.appspotmail.com

Oops: divide error: 0000 [#1] SMP KASAN NOPTI
CPU: 0 UID: 0 PID: 6029 Comm: syz-executor518 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
RIP: 0010:add_device drivers/mtd/devices/block2mtd.c:296 [inline]
RIP: 0010:block2mtd_setup2.isra.0+0x3c8/0xc70 drivers/mtd/devices/block2mtd.c:459
Code: 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 2b 08 00 00 48 8b 6d 08 31 ff 48 89 e8 48 c1 e0 09 48 99 <49> f7 ff 48 89 d6 48 89 54 24 10 e8 98 d5 4d fb 48 8b 54 24 10 48
RSP: 0018:ffffc90004ccf9f0 EFLAGS: 00010206
RAX: 0000000000100000 RBX: 1ffff92000999f41 RCX: ffffffff86bc9838
RDX: 0000000000000000 RSI: ffffffff86bc984a RDI: 0000000000000000
RBP: 0000000000000800 R08: 0000000000000005 R09: 000000000000001f
R10: 0000000000000007 R11: 0000000000000000 R12: ffffc90004ccfaa8
R13: 0000000000000000 R14: ffff8880254fe000 R15: 0000000000000000
FS:  000055558148e400(0000) GS:ffff8880d5dec000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055a8208cda78 CR3: 000000003ad58000 CR4: 0000000000352ef0
Call Trace:
 <TASK>
 block2mtd_setup+0xbd/0xd0 drivers/mtd/devices/block2mtd.c:476
 param_attr_store+0x199/0x300 kernel/params.c:589
 module_attr_store+0x58/0x80 kernel/params.c:904
 sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:145
 kernfs_fop_write_iter+0x3e0/0x5f0 fs/kernfs/file.c:345
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x6ac/0x1050 fs/read_write.c:687
 ksys_write+0x12a/0x250 fs/read_write.c:739
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f0b39a14737
Code: 48 89 fa 4c 89 df e8 98 1d 00 00 8b 93 08 03 00 00 59 5e 48 83 f8 fc 74 1a 5b c3 0f 1f 84 00 00 00 00 00 48 8b 44 24 10 0f 05 <5b> c3 0f 1f 80 00 00 00 00 83 e2 39 83 fa 08 75 de e8 23 ff ff ff
RSP: 002b:00007ffdcc22a9a0 EFLAGS: 00000202 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 000055558148e400 RCX: 00007f0b39a14737
RDX: 000000000000000c RSI: 00007ffdcc22aa50 RDI: 0000000000000004
RBP: 0000000000000003 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 00007ffdcc22aa50
R13: 00007ffdcc22aa10 R14: 00007ffdcc22a9f0 R15: 0000000000000002
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:add_device drivers/mtd/devices/block2mtd.c:296 [inline]
RIP: 0010:block2mtd_setup2.isra.0+0x3c8/0xc70 drivers/mtd/devices/block2mtd.c:459
Code: 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 2b 08 00 00 48 8b 6d 08 31 ff 48 89 e8 48 c1 e0 09 48 99 <49> f7 ff 48 89 d6 48 89 54 24 10 e8 98 d5 4d fb 48 8b 54 24 10 48
RSP: 0018:ffffc90004ccf9f0 EFLAGS: 00010206
RAX: 0000000000100000 RBX: 1ffff92000999f41 RCX: ffffffff86bc9838
RDX: 0000000000000000 RSI: ffffffff86bc984a RDI: 0000000000000000
RBP: 0000000000000800 R08: 0000000000000005 R09: 000000000000001f
R10: 0000000000000007 R11: 0000000000000000 R12: ffffc90004ccfaa8
R13: 0000000000000000 R14: ffff8880254fe000 R15: 0000000000000000
FS:  000055558148e400(0000) GS:ffff8880d5dec000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055a8208cda78 CR3: 000000003ad58000 CR4: 0000000000352ef0
----------------
Code disassembly (best guess):
   0:	48 b8 00 00 00 00 00 	movabs $0xdffffc0000000000,%rax
   7:	fc ff df
   a:	48 89 fa             	mov    %rdi,%rdx
   d:	48 c1 ea 03          	shr    $0x3,%rdx
  11:	80 3c 02 00          	cmpb   $0x0,(%rdx,%rax,1)
  15:	0f 85 2b 08 00 00    	jne    0x846
  1b:	48 8b 6d 08          	mov    0x8(%rbp),%rbp
  1f:	31 ff                	xor    %edi,%edi
  21:	48 89 e8             	mov    %rbp,%rax
  24:	48 c1 e0 09          	shl    $0x9,%rax
  28:	48 99                	cqto
* 2a:	49 f7 ff             	idiv   %r15 <-- trapping instruction
  2d:	48 89 d6             	mov    %rdx,%rsi
  30:	48 89 54 24 10       	mov    %rdx,0x10(%rsp)
  35:	e8 98 d5 4d fb       	call   0xfb4dd5d2
  3a:	48 8b 54 24 10       	mov    0x10(%rsp),%rdx
  3f:	48                   	rex.W


---
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.

[PATCH v2] mtd: block2mtd: Fix divide error when erase_size is zero

[Pei Xiao]

#syz test

The erase size is parsed from the "block2mtd" module parameter and can
be set to zero. add_device() then evaluates

        if (size % erase_size)

with a zero divisor, which triggers a divide error:

        divide error: 0000 [#1] PREEMPT SMP PTI
        RIP: 0010:add_device drivers/mtd/devices/block2mtd.c:296 [inline]
        RIP: 0010:block2mtd_setup2+0x592/0xda0 drivers/mtd/devices/block2mtd.c:459
        Call Trace:
         block2mtd_setup+0x27/0xe0 drivers/mtd/devices/block2mtd.c:476
         param_attr_store+0x214/0x310 kernel/params.c:589
         module_attr_store+0x65/0x90 kernel/params.c:904
         kernfs_fop_write_iter+0x3a4/0x540 fs/kernfs/file.c:345
         ...

Reject a zero erase size before performing the modulo operation so the
existing "erasesize must be a divisor of device size" error path
reports the invalid argument and frees the device.

While at it, drop the unnecessary (long) cast from the size operand of
the modulo.

Fixes: ea6d833a3fdd ("mtd: block2mtd: check device size")
Reported-by: syzbot+b320a4d5f65a61dbbf89@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/lkml/6a7b58ba.ac361c09.22ff0a.0045.GAE@google.com/
Suggested-by: Jörn Engel <joern@barelysecure.org>
Cc: stable@vger.kernel.org
Signed-off-by: Pei Xiao <xiaopei01@kylinos.cn>
---
changlogs in v2:
1.Add Suggested-by tag
2.remove unnecessary (long) cast from the size
---
 drivers/mtd/devices/block2mtd.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/mtd/devices/block2mtd.c b/drivers/mtd/devices/block2mtd.c
index 03e80b2c4f5a..3e2367dfff88 100644
--- a/drivers/mtd/devices/block2mtd.c
+++ b/drivers/mtd/devices/block2mtd.c
@@ -293,7 +293,7 @@ static struct block2mtd_dev *add_device(char *devname, int erase_size,
 	}
 
 	size = bdev_nr_bytes(bdev);
-	if ((long)size % erase_size) {
+	if (!erase_size || size % erase_size) {
 		pr_err("erasesize must be a divisor of device size\n");
 		goto err_free_block2mtd;
 	}
-- 
2.25.1

Re: [syzbot] [mtd?] divide error in block2mtd_setup2

[syzbot]

Hello,

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

Reported-by: syzbot+b320a4d5f65a61dbbf89@syzkaller.appspotmail.com
Tested-by: syzbot+b320a4d5f65a61dbbf89@syzkaller.appspotmail.com

Tested on:

commit:         f5bbbfec Merge tag 'probes-fixes-v7.2-rc7' of git://gi..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1336f879580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=c44651ea7dd2f307
dashboard link: https://syzkaller.appspot.com/bug?extid=b320a4d5f65a61dbbf89
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
patch:          https://syzkaller.appspot.com/x/patch.diff?x=13241479580000

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