io_uring: reexpand under-reexpanded iters
[ 74.211232] BUG: KASAN: stack-out-of-bounds in iov_iter_revert+0x809/0x900 [ 74.212778] Read of size 8 at addr ffff888025dc78b8 by task syz-executor.0/828 [ 74.214756] CPU: 0 PID: 828 Comm: syz-executor.0 Not tainted 5.14.0-rc3-next-20210730 #1 [ 74.216525] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014 [ 74.219033] Call Trace: [ 74.219683] dump_stack_lvl+0x8b/0xb3 [ 74.220706] print_address_description.constprop.0+0x1f/0x140 [ 74.224226] kasan_report.cold+0x7f/0x11b [ 74.226085] iov_iter_revert+0x809/0x900 [ 74.227960] io_write+0x57d/0xe40 [ 74.232647] io_issue_sqe+0x4da/0x6a80 [ 74.242578] __io_queue_sqe+0x1ac/0xe60 [ 74.245358] io_submit_sqes+0x3f6e/0x76a0 [ 74.248207] __do_sys_io_uring_enter+0x90c/0x1a20 [ 74.257167] do_syscall_64+0x3b/0x90 [ 74.257984] entry_SYSCALL_64_after_hwframe+0x44/0xae old_size = iov_iter_count(); ... iov_iter_revert(old_size - iov_iter_count()); If iov_iter_revert() is done base on the initial size as above, and the iter is truncated and not reexpanded in the middle, it miscalculates borders causing problems. This trace is due to no one reexpanding after generic_write_checks(). Now iters store how many bytes has been truncated, so reexpand them to the initial state right before reverting. Cc: stable@vger.kernel.org Reported-by:Palash Oswal <oswalpalash@gmail.com> Reported-by:
Sudip Mukherjee <sudipm.mukherjee@gmail.com> Reported-and-tested-by:
<syzbot+9671693590ef5aad8953@syzkaller.appspotmail.com> Signed-off-by:
Pavel Begunkov <asml.silence@gmail.com> Signed-off-by:
Al Viro <viro@zeniv.linux.org.uk>
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2112ff5c
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