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SubjectRe: [PATCH] fs: Fix UBSAN detected shift-out-bounds error for bad superblock
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在 2022/11/14 19:04, Jan Kara 写道:
> On Mon 14-11-22 10:49:57, Liao Chang wrote:
>> UBSAN: shift-out-of-bounds in fs/minix/bitmap.c:103:3
>> shift exponent 8192 is too large for 32-bit type 'unsigned int'
>> CPU: 1 PID: 32273 Comm: syz-executor.0 Tainted: G W
>> 6.1.0-rc4-dirty #11
>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
>> BIOS rel-1.15.0-0-g2dd4b9b3f840-prebuilt.qemu.org 04/01/2014
>> Call Trace:
>> <TASK>
>> dump_stack_lvl+0xcd/0x134
>> ubsan_epilogue+0xb/0x50
>> __ubsan_handle_shift_out_of_bounds.cold+0xb1/0x18d
>> minix_count_free_blocks.cold+0x16/0x1b
>> minix_statfs+0x22a/0x490
>> statfs_by_dentry+0x133/0x210
>> user_statfs+0xa9/0x160
>> __do_sys_statfs+0x7a/0xf0
>> do_syscall_64+0x35/0x80
>> entry_SYSCALL_64_after_hwframe+0x63/0xcd
>>
>> The superblock stores on disk contains the size of a data zone, which is
>> too large to used as the shift when kernel try to calculate the total
>> size of zones, so it needs to check the superblock when kernel mounts
>> MINIX-FS.
>>
>> Signed-off-by: Liao Chang <liaochang1@huawei.com>
>
> Thanks for the patch. Just one nit:
>
>> diff --git a/fs/minix/inode.c b/fs/minix/inode.c
>> index da8bdd1712a7..f1d1c2312817 100644
>> --- a/fs/minix/inode.c
>> +++ b/fs/minix/inode.c
>> @@ -166,6 +166,12 @@ static bool minix_check_superblock(struct super_block *sb)
>> sb->s_maxbytes > (7 + 512 + 512*512) * BLOCK_SIZE)
>> return false;
>>
>> + /* the total size of zones must no exceed the limitation of U32_MAX. */
>> + if (sbi->s_log_zone_size && (sbi->s_nzones - sbi->s_firstdatazone) &&
>> + (__builtin_clzl((__u32)(sbi->s_nzones - sbi->s_firstdatazone)) <=
>
> Why this strange __builtin_clzl() function? We have a ffs() function in
> the kernel for this :)

Great suggestion, i should use a compiler neutral API to caclulate leading zero count,
what about count_leading_zeros()?

Thanks.

>
> Honza
>
>> + sbi->s_log_zone_size))
>> + return false;
>> +
>> return true;
>> }
>>
>> --
>> 2.17.1
>>

--
BR,
Liao, Chang

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