memory leak in vhost_net_ioctl

[syzbot <syzbot+0789f0c7e45efd7bb643@xxxxxxxxxxxxxxxxxxxxxxxxx>]

Hello,

syzbot found the following crash on:

HEAD commit:    788a0249 Merge tag 'arc-5.2-rc4' of git://git.kernel.org/p..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15dc9ea6a00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=d5c73825cbdc7326
dashboard link: https://syzkaller.appspot.com/bug?extid=0789f0c7e45efd7bb643
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10b31761a00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=124892c1a00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+0789f0c7e45efd7bb643@xxxxxxxxxxxxxxxxxxxxxxxxx

udit: type=1400 audit(1559768703.229:36): avc:  denied  { map } for   
pid=7116 comm="syz-executor330" path="/root/syz-executor330334897"  
dev="sda1" ino=16461 scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023  
tcontext=unconfined_u:object_r:user_home_t:s0 tclass=file permissive=1
executing program
executing program
BUG: memory leak
unreferenced object 0xffff88812421fe40 (size 64):
  comm "syz-executor330", pid 7117, jiffies 4294949245 (age 13.030s)
  hex dump (first 32 bytes):
    01 00 00 00 20 69 6f 63 00 00 00 00 64 65 76 2f  .... ioc....dev/
    50 fe 21 24 81 88 ff ff 50 fe 21 24 81 88 ff ff  P.!$....P.!$....
  backtrace:
    [<00000000ae0c4ae0>] kmemleak_alloc_recursive  
include/linux/kmemleak.h:55 [inline]
    [<00000000ae0c4ae0>] slab_post_alloc_hook mm/slab.h:439 [inline]
    [<00000000ae0c4ae0>] slab_alloc mm/slab.c:3326 [inline]
    [<00000000ae0c4ae0>] kmem_cache_alloc_trace+0x13d/0x280 mm/slab.c:3553
    [<0000000079ebab38>] kmalloc include/linux/slab.h:547 [inline]
    [<0000000079ebab38>] vhost_net_ubuf_alloc drivers/vhost/net.c:241  
[inline]
    [<0000000079ebab38>] vhost_net_set_backend drivers/vhost/net.c:1534  
[inline]
    [<0000000079ebab38>] vhost_net_ioctl+0xb43/0xc10  
drivers/vhost/net.c:1716
    [<000000009f6204a2>] vfs_ioctl fs/ioctl.c:46 [inline]
    [<000000009f6204a2>] file_ioctl fs/ioctl.c:509 [inline]
    [<000000009f6204a2>] do_vfs_ioctl+0x62a/0x810 fs/ioctl.c:696
    [<00000000b45866de>] ksys_ioctl+0x86/0xb0 fs/ioctl.c:713
    [<00000000dfb41eb8>] __do_sys_ioctl fs/ioctl.c:720 [inline]
    [<00000000dfb41eb8>] __se_sys_ioctl fs/ioctl.c:718 [inline]
    [<00000000dfb41eb8>] __x64_sys_ioctl+0x1e/0x30 fs/ioctl.c:718
    [<0000000049c1f547>] do_syscall_64+0x76/0x1a0  
arch/x86/entry/common.c:301
    [<0000000029cc8ca7>] entry_SYSCALL_64_after_hwframe+0x44/0xa9

BUG: memory leak
unreferenced object 0xffff88812421fa80 (size 64):
  comm "syz-executor330", pid 7130, jiffies 4294949755 (age 7.930s)
  hex dump (first 32 bytes):
    01 00 00 00 01 00 00 00 00 00 00 00 2f 76 69 72  ............/vir
    90 fa 21 24 81 88 ff ff 90 fa 21 24 81 88 ff ff  ..!$......!$....
  backtrace:
    [<00000000ae0c4ae0>] kmemleak_alloc_recursive  
include/linux/kmemleak.h:55 [inline]
    [<00000000ae0c4ae0>] slab_post_alloc_hook mm/slab.h:439 [inline]
    [<00000000ae0c4ae0>] slab_alloc mm/slab.c:3326 [inline]
    [<00000000ae0c4ae0>] kmem_cache_alloc_trace+0x13d/0x280 mm/slab.c:3553
    [<0000000079ebab38>] kmalloc include/linux/slab.h:547 [inline]
    [<0000000079ebab38>] vhost_net_ubuf_alloc drivers/vhost/net.c:241  
[inline]
    [<0000000079ebab38>] vhost_net_set_backend drivers/vhost/net.c:1534  
[inline]
    [<0000000079ebab38>] vhost_net_ioctl+0xb43/0xc10  
drivers/vhost/net.c:1716
    [<000000009f6204a2>] vfs_ioctl fs/ioctl.c:46 [inline]
    [<000000009f6204a2>] file_ioctl fs/ioctl.c:509 [inline]
    [<000000009f6204a2>] do_vfs_ioctl+0x62a/0x810 fs/ioctl.c:696
    [<00000000b45866de>] ksys_ioctl+0x86/0xb0 fs/ioctl.c:713
    [<00000000dfb41eb8>] __do_sys_ioctl fs/ioctl.c:720 [inline]
    [<00000000dfb41eb8>] __se_sys_ioctl fs/ioctl.c:718 [inline]
    [<00000000dfb41eb8>] __x64_sys_ioctl+0x1e/0x30 fs/ioctl.c:718
    [<0000000049c1f547>] do_syscall_64+0x76/0x1a0  
arch/x86/entry/common.c:301
    [<0000000029cc8ca7>] entry_SYSCALL_64_after_hwframe+0x44/0xa9



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