memory leak in xskq_create

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: a68a0262 mm/madvise: remove racy mm ownership check
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=165b9413500000
kernel config: https://syzkaller.appspot.com/x/.config?x=4305fa9ea70c7a9f
dashboard link: https://syzkaller.appspot.com/bug?extid=cfa88ddd0655afa88763
compiler: gcc (GCC) 10.1.0-syz 20200507
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1180a237500000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=114067cf500000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+cfa88d...@syzkaller.appspotmail.com

Debian GNU/Linux 9 syzkaller ttyS0
Warning: Permanently added '10.128.0.50' (ECDSA) to the list of known hosts.
executing program
executing program
BUG: memory leak
unreferenced object 0xffff88810f897940 (size 64):
comm "syz-executor991", pid 8502, jiffies 4294942194 (age 14.080s)
hex dump (first 32 bytes):
7f 00 00 00 80 00 00 00 00 00 00 00 00 00 00 00 ................
00 a0 37 0c 81 88 ff ff 00 00 00 00 00 00 00 00 ..7.............
backtrace:
[<00000000639d0dd1>] xskq_create+0x23/0xd0 include/linux/slab.h:552
[<00000000b680b035>] xsk_init_queue net/xdp/xsk.c:508 [inline]
[<00000000b680b035>] xsk_setsockopt+0x1c4/0x590 net/xdp/xsk.c:875
[<000000002b302260>] __sys_setsockopt+0x1b0/0x360 net/socket.c:2132
[<00000000ae03723e>] __do_sys_setsockopt net/socket.c:2143 [inline]
[<00000000ae03723e>] __se_sys_setsockopt net/socket.c:2140 [inline]
[<00000000ae03723e>] __x64_sys_setsockopt+0x22/0x30 net/socket.c:2140
[<0000000005c2b4a0>] do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
[<0000000003db140f>] entry_SYSCALL_64_after_hwframe+0x44/0xa9

BUG: memory leak
unreferenced object 0xffff88810f8979c0 (size 64):
comm "syz-executor991", pid 8503, jiffies 4294942194 (age 14.080s)
hex dump (first 32 bytes):
ff 03 00 00 00 04 00 00 00 00 00 00 00 00 00 00 ................
00 00 13 12 81 88 ff ff 00 00 00 00 00 00 00 00 ................
backtrace:
[<00000000639d0dd1>] xskq_create+0x23/0xd0 include/linux/slab.h:552
[<00000000b680b035>] xsk_init_queue net/xdp/xsk.c:508 [inline]
[<00000000b680b035>] xsk_setsockopt+0x1c4/0x590 net/xdp/xsk.c:875
[<000000002b302260>] __sys_setsockopt+0x1b0/0x360 net/socket.c:2132
[<00000000ae03723e>] __do_sys_setsockopt net/socket.c:2143 [inline]
[<00000000ae03723e>] __se_sys_setsockopt net/socket.c:2140 [inline]
[<00000000ae03723e>] __x64_sys_setsockopt+0x22/0x30 net/socket.c:2140
[<0000000005c2b4a0>] do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
[<0000000003db140f>] entry_SYSCALL_64_after_hwframe+0x44/0xa9



---
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[Peilin Ye]

Hi all,

On Sun, Dec 13, 2020 at 06:53:10AM -0800, syzbot wrote:
> BUG: memory leak
> unreferenced object 0xffff88810f897940 (size 64):
> comm "syz-executor991", pid 8502, jiffies 4294942194 (age 14.080s)
> hex dump (first 32 bytes):
> 7f 00 00 00 80 00 00 00 00 00 00 00 00 00 00 00 ................
> 00 a0 37 0c 81 88 ff ff 00 00 00 00 00 00 00 00 ..7.............
> backtrace:
> [<00000000639d0dd1>] xskq_create+0x23/0xd0 include/linux/slab.h:552
> [<00000000b680b035>] xsk_init_queue net/xdp/xsk.c:508 [inline]
> [<00000000b680b035>] xsk_setsockopt+0x1c4/0x590 net/xdp/xsk.c:875
> [<000000002b302260>] __sys_setsockopt+0x1b0/0x360 net/socket.c:2132
> [<00000000ae03723e>] __do_sys_setsockopt net/socket.c:2143 [inline]
> [<00000000ae03723e>] __se_sys_setsockopt net/socket.c:2140 [inline]
> [<00000000ae03723e>] __x64_sys_setsockopt+0x22/0x30 net/socket.c:2140
> [<0000000005c2b4a0>] do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
> [<0000000003db140f>] entry_SYSCALL_64_after_hwframe+0x44/0xa9

I have tested the following diff locally against syzbot's reproducer,
and sent a patch to it [1] for testing. I will send a real patch here
tomorrow if syzbot is happy about it. Please see explanation below.

--- a/net/xdp/xsk_buff_pool.c
+++ b/net/xdp/xsk_buff_pool.c
@@ -37,6 +37,9 @@ void xp_destroy(struct xsk_buff_pool *pool)
if (!pool)
return;

+ xskq_destroy(pool->fq);
+ xskq_destroy(pool->cq);
+
kvfree(pool->heads);
kvfree(pool);
}
@@ -234,16 +237,6 @@ static void xp_release_deferred(struct work_struct *work)
xp_clear_dev(pool);
rtnl_unlock();

- if (pool->fq) {
- xskq_destroy(pool->fq);
- pool->fq = NULL;
- }
-
- if (pool->cq) {
- xskq_destroy(pool->cq);
- pool->cq = NULL;
- }
-
xdp_put_umem(pool->umem, false);
xp_destroy(pool);
}

When xsk_bind() allocates `xs->pool` but something else goes wrong:

xs->pool = xp_create_and_assign_umem(xs, xs->umem);
[...]
if (err) {
xp_destroy(xs->pool);

xp_destroy() doesn't free `pool->{f,c}q`, causing a memory leak. Move
`xskq_destroy(pool->{f,c}q)` from xp_release_deferred() to xp_destroy().

Also, since xskq_destroy() already does null check, I think it's
unnecessary to do it again here?

Thanks,
Peilin Ye

[1] https://syzkaller.appspot.com/bug?id=fea808dfe3c6dfdd6ba9778becbffe0b14e91294

[Björn Töpel]

On 2020-12-16 19:11, Peilin Ye wrote:
> Hi all,
>
> On Sun, Dec 13, 2020 at 06:53:10AM -0800, syzbot wrote:
>> BUG: memory leak
>> unreferenced object 0xffff88810f897940 (size 64):
>> comm "syz-executor991", pid 8502, jiffies 4294942194 (age 14.080s)
>> hex dump (first 32 bytes):
>> 7f 00 00 00 80 00 00 00 00 00 00 00 00 00 00 00 ................
>> 00 a0 37 0c 81 88 ff ff 00 00 00 00 00 00 00 00 ..7.............
>> backtrace:
>> [<00000000639d0dd1>] xskq_create+0x23/0xd0 include/linux/slab.h:552
>> [<00000000b680b035>] xsk_init_queue net/xdp/xsk.c:508 [inline]
>> [<00000000b680b035>] xsk_setsockopt+0x1c4/0x590 net/xdp/xsk.c:875
>> [<000000002b302260>] __sys_setsockopt+0x1b0/0x360 net/socket.c:2132
>> [<00000000ae03723e>] __do_sys_setsockopt net/socket.c:2143 [inline]
>> [<00000000ae03723e>] __se_sys_setsockopt net/socket.c:2140 [inline]
>> [<00000000ae03723e>] __x64_sys_setsockopt+0x22/0x30 net/socket.c:2140
>> [<0000000005c2b4a0>] do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
>> [<0000000003db140f>] entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> I have tested the following diff locally against syzbot's reproducer,
> and sent a patch to it [1] for testing. I will send a real patch here
> tomorrow if syzbot is happy about it. Please see explanation below.
>

Hi Peilin Ye!

Thanks for taking a look! Magnus has already addressed this problem in
another patch [1].


Cheers,
Björn



[1]
https://lore.kernel.org/bpf/20201214085127.396...@gmail.com/

[Peilin Ye]

Hi Björn,

No problem! Oops, I searched for "cfa88ddd0655afa88763" on LKML and
didn't notice Magnus's patch. I should have searched netdev too.

Thanks,
Peilin Ye