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 <jack@xxxxxxxx> SUSE Labs, CR
