memory leak in rw_copy_check_uvector

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    da2968ff Merge tag 'pci-v5.9-fixes-1' of git://git.kernel...
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=124577f9900000
kernel config:  https://syzkaller.appspot.com/x/.config?x=948134d9ff96e950
dashboard link: https://syzkaller.appspot.com/bug?extid=6e14de8b553308b5507c
compiler:       gcc (GCC) 10.1.0-syz 20200507
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12a9ab36900000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17049fa1900000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+6e14de8b553308b5507c@xxxxxxxxxxxxxxxxxxxxxxxxx

BUG: memory leak
unreferenced object 0xffff88811c405400 (size 1024):
  comm "syz-executor386", pid 6503, jiffies 4294942347 (age 13.130s)
  hex dump (first 32 bytes):
    00 01 00 20 00 00 00 00 14 00 00 00 00 00 00 00  ... ............
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
  backtrace:
    [<000000001a62dd57>] kmalloc_array include/linux/slab.h:594 [inline]
    [<000000001a62dd57>] rw_copy_check_uvector+0x171/0x1a0 fs/read_write.c:812
    [<0000000016ad020b>] import_iovec+0x4a/0x140 lib/iov_iter.c:1681
    [<00000000fb58399a>] io_import_iovec+0x271/0x640 fs/io_uring.c:2879
    [<0000000002d03b50>] io_rw_prep_async fs/io_uring.c:3006 [inline]
    [<0000000002d03b50>] io_read_prep+0x94/0xf0 fs/io_uring.c:3031
    [<000000008ab01d5d>] io_req_defer_prep fs/io_uring.c:5462 [inline]
    [<000000008ab01d5d>] io_req_defer_prep+0x1c6/0x720 fs/io_uring.c:5442
    [<0000000075ed8a70>] io_submit_sqe fs/io_uring.c:6262 [inline]
    [<0000000075ed8a70>] io_submit_sqes+0x306/0xc00 fs/io_uring.c:6488
    [<00000000d1d617da>] __do_sys_io_uring_enter+0x582/0x830 fs/io_uring.c:8265
    [<00000000334cee0e>] do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
    [<0000000053cdb89f>] entry_SYSCALL_64_after_hwframe+0x44/0xa9



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