[PATCH] ubi: Reject device with erasesize 0

[Jan Kara]

In principle MTD device with erasesize 0 can exist and it is possible to
create them e.g. via KVM. If that happens UBI layer currently crashes
with:

ubi7: attaching mtd147
divide error: 0000 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 20023 Comm: syz-executor.0 Not tainted 6.2.0 #6
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
1.13.0-1ubuntu1.1 04/01/2014
RIP: 0010:mtd_div_by_eb include/linux/mtd/mtd.h:580 [inline]
RIP: 0010:io_init drivers/mtd/ubi/build.c:620 [inline]
RIP: 0010:ubi_attach_mtd_dev+0x77f/0x2fe0 drivers/mtd/ubi/build.c:955
Code: fc ff df 48 c1 ea 03 0f b6 14 02 4c 89 f0 83 e0 07 83 c0 03 38
d0 7c 08 84 d2 0f 85 1f 25 00 00 41 8b 4c 24 10 48 89 d8 31 d2 <48> f7
f1 48 89 c3 e8 b6 f3 1b fc 48 8d 85 40 17 00 00 48 89 c2 48
RSP: 0018:ffffc9000be0fd30 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffff888047a49d40 RDI: 0000000000000002
RBP: ffff888024e1c000 R08: 0000000000000016 R09: fffff520017c1f47
R10: ffffc9000be0fa37 R11: fffff520017c1f46 R12: ffff88806545a000
R13: 0000000000000000 R14: ffff88806545a010 R15: 0000000000000007
FS:  00007fd45e85c700(0000) GS:ffff88802ca00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f64aeef53a4 CR3: 000000004f39a000 CR4: 0000000000350ef0
Call Trace:
 <TASK>
 ctrl_cdev_ioctl+0x303/0x3a0 drivers/mtd/ubi/cdev.c:1043
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl fs/ioctl.c:856 [inline]
 __x64_sys_ioctl+0x198/0x210 fs/ioctl.c:856
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

Handle such devices gracefully and just reject attaching UBI to them
instead of crashing.

Reported-by: Yu Hao <yhao016 at ucr.edu>
Link: https://lore.kernel.org/all/CA+UBctDsHRpkLG5ppdiuV8Msn4Dx-ZJ2xDrxfa48VMb7ZE+xBA@mail.gmail.com
Signed-off-by: Jan Kara <jack at suse.cz>
---
 drivers/mtd/ubi/build.c | 3 +++
 1 file changed, 3 insertions(+)

It doesn't seem the discussion linked above concluded in a patch. So is
anything wrong with the trivial approach here so that we can close the issue?

diff --git a/drivers/mtd/ubi/build.c b/drivers/mtd/ubi/build.c
index 8b91a55ec0d2..684273e13efb 100644
--- a/drivers/mtd/ubi/build.c
+++ b/drivers/mtd/ubi/build.c
@@ -613,6 +613,9 @@ static int io_init(struct ubi_device *ubi, int max_beb_per1024)
 	if (ubi->vid_hdr_offset < 0)
 		return -EINVAL;
 
+	if (ubi->mtd->erasesize == 0)
+		return -EINVAL;
+
 	/*
 	 * Note, in this implementation we support MTD devices with 0x7FFFFFFF
 	 * physical eraseblocks maximum.
-- 
2.35.3