Messages in this thread | | | Subject | Re: [PATCH net] kcm: Fix memory leak in error path of kcm_sendmsg() | From | Paolo Abeni <> | Date | Tue, 05 Sep 2023 10:09:43 +0200 |
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Hello,
On Sun, 2023-09-03 at 01:52 +0900, Shigeru Yoshida wrote: > syzbot reported a memory leak like below [1]: > > BUG: memory leak > unreferenced object 0xffff88810b088c00 (size 240): > comm "syz-executor186", pid 5012, jiffies 4294943306 (age 13.680s) > hex dump (first 32 bytes): > 00 89 08 0b 81 88 ff ff 00 00 00 00 00 00 00 00 ................ > 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ > backtrace: > [<ffffffff83e5d5ff>] __alloc_skb+0x1ef/0x230 net/core/skbuff.c:634 > [<ffffffff84606e59>] alloc_skb include/linux/skbuff.h:1289 [inline] > [<ffffffff84606e59>] kcm_sendmsg+0x269/0x1050 net/kcm/kcmsock.c:815 > [<ffffffff83e479c6>] sock_sendmsg_nosec net/socket.c:725 [inline] > [<ffffffff83e479c6>] sock_sendmsg+0x56/0xb0 net/socket.c:748 > [<ffffffff83e47f55>] ____sys_sendmsg+0x365/0x470 net/socket.c:2494 > [<ffffffff83e4c389>] ___sys_sendmsg+0xc9/0x130 net/socket.c:2548 > [<ffffffff83e4c536>] __sys_sendmsg+0xa6/0x120 net/socket.c:2577 > [<ffffffff84ad7bb8>] do_syscall_x64 arch/x86/entry/common.c:50 [inline] > [<ffffffff84ad7bb8>] do_syscall_64+0x38/0xb0 arch/x86/entry/common.c:80 > [<ffffffff84c0008b>] entry_SYSCALL_64_after_hwframe+0x63/0xcd > > In kcm_sendmsg(), newly allocated socket buffers can be added to skb->next. If > an error occurred and jumped to out_error label, those newly allocated socket > buffers can be leaked. This patch fixes this issue by remembering the last > allocated socket buffer in kcm_tx_msg(head)->last_skb.
I think the root cause should be clarified a little more. When the 'head' skb will be freed, all the frag_list skbs will be released, too.
AFAICS the issue is that in case of error after copying some bytes, kcm_tx_msg(head)->last_skb is left unmodified and such reference is used as the cursor to append newly allocated skbs to 'head'.
A later kcm_sendmsg will use an obsoleted 'last_skb' reference, corrupting the 'head' frag_list and causing the leak.
The fix looks correct, but could you please send a v2 with an updated/more extensive commit message?
> Link: https://syzkaller.appspot.com/bug?extid=6f98de741f7dbbfc4ccb [1] > Reported-by: syzbot+6f98de741f7dbbfc4ccb@syzkaller.appspotmail.com > Fixes: ab7ac4eb9832 ("kcm: Kernel Connection Multiplexor module") > Signed-off-by: Shigeru Yoshida <syoshida@redhat.com>
Additionally please feed the patch to syzbot, so it can verify the fix, and add the relevant tag.
Thanks,
Paolo
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