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Message-ID: <e781f927-07f4-9165-1123-f9b501c552b1@infradead.org>
Date: Mon, 14 Nov 2022 13:09:06 -0800
From: Randy Dunlap <rdunlap@...radead.org>
To: Liao Chang <liaochang1@...wei.com>, willy@...radead.org,
damien.lemoal@...nsource.wdc.com, akpm@...ux-foundation.org,
jack@...e.cz, qhjin.dev@...il.com, songmuchun@...edance.com
Cc: linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fs: Fix UBSAN detected shift-out-bounds error for bad
superblock
On 11/13/22 18:49, 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@...wei.com>
> ---
> fs/minix/inode.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> 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. */
must not exceed
> + if (sbi->s_log_zone_size && (sbi->s_nzones - sbi->s_firstdatazone) &&
> + (__builtin_clzl((__u32)(sbi->s_nzones - sbi->s_firstdatazone)) <=
> + sbi->s_log_zone_size))
> + return false;
> +
> return true;
> }
>
--
~Randy
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