On Tue 07-05-24 23:17:57, Justin Stitt wrote:
> Running syzkaller with the newly enabled signed integer overflow
> sanitizer produces this report:
>
> [ 195.401651] ------------[ cut here ]------------
> [ 195.404808] UBSAN: signed-integer-overflow in ../fs/open.c:321:15
> [ 195.408739] 9223372036854775807 + 562984447377399 cannot be represented in
> type 'loff_t' (aka 'long long')
> [ 195.414683] CPU: 1 PID: 703 Comm: syz-executor.0 Not tainted
> 6.8.0-rc2-00039-g14de58dbe653-dirty #11
> [ 195.420138] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
> 1.16.3-debian-1.16.3-2 04/01/2014
> [ 195.425804] Call Trace:
> [ 195.427360] <TASK>
> [ 195.428791] dump_stack_lvl+0x93/0xd0
> [ 195.431150] handle_overflow+0x171/0x1b0
> [ 195.433640] vfs_fallocate+0x459/0x4f0
Well, we compile the kernel with -fno-strict-overflow for a reason so I
wouldn't consider this a bug. But check_add_overflow() is easier to digest
since we don't have to worry about type details so I'm for this change.
> @@ -319,8 +320,12 @@ int vfs_fallocate(struct file *file, int mode, loff_t
> offset, loff_t len)
> if (!S_ISREG(inode->i_mode) && !S_ISBLK(inode->i_mode))
> return -ENODEV;
>
> - /* Check for wrap through zero too */
> - if (((offset + len) > inode->i_sb->s_maxbytes) || ((offset + len) < 0))
> + /* Check for wraparound */
> + if (check_add_overflow(offset, len, &sum))
> + return -EFBIG;
> +
> + /* Now, check bounds */
> + if (sum > inode->i_sb->s_maxbytes || sum < 0)
> return -EFBIG;
But why do you check for sum < 0? We know from previous checks offset >= 0
&& len > 0 so unless we overflow, sum is guaranteed to be > 0.
Honza
--
Jan Kara <[email protected]>
SUSE Labs, CR
