Commit 34b88a68 authored Mar 14, 2016 by Arnaldo Carvalho de Melo Committed by David S. Miller Mar 14, 2016

net: Fix use after free in the recvmmsg exit path



The syzkaller fuzzer hit the following use-after-free:

  Call Trace:
   [<ffffffff8175ea0e>] __asan_report_load8_noabort+0x3e/0x40 mm/kasan/report.c:295
   [<ffffffff851cc31a>] __sys_recvmmsg+0x6fa/0x7f0 net/socket.c:2261
   [<     inline     >] SYSC_recvmmsg net/socket.c:2281
   [<ffffffff851cc57f>] SyS_recvmmsg+0x16f/0x180 net/socket.c:2270
   [<ffffffff86332bb6>] entry_SYSCALL_64_fastpath+0x16/0x7a
  arch/x86/entry/entry_64.S:185

And, as Dmitry rightly assessed, that is because we can drop the
reference and then touch it when the underlying recvmsg calls return
some packets and then hit an error, which will make recvmmsg to set
sock->sk->sk_err, oops, fix it.

Reported-and-Tested-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Kostya Serebryany <kcc@google.com>
Cc: Sasha Levin <sasha.levin@oracle.com>
Fixes: a2e27255 ("net: Introduce recvmmsg socket syscall")
http://lkml.kernel.org/r/20160122211644.GC2470@redhat.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent b6e40382

net/socket.c

+19 −19

Original line number	Diff line number	Diff line
		@@ -2244,13 +2244,14 @@ int __sys_recvmmsg(int fd, struct mmsghdr __user *mmsg, unsigned int vlen,
		cond_resched();
		}

		out_put:
		fput_light(sock->file, fput_needed);

		if (err == 0)
		return datagrams;
		goto out_put;

		if (datagrams == 0) {
		datagrams = err;
		goto out_put;
		}

		if (datagrams != 0) {
		/*
		* We may return less entries than requested (vlen) if the
		* sock is non block and there aren't enough datagrams...
		@@ -2264,13 +2265,12 @@ out_put:
		*/
		sock->sk->sk_err = -err;
		}
		out_put:
		fput_light(sock->file, fput_needed);

		return datagrams;
		}

		return err;
		}

		SYSCALL_DEFINE5(recvmmsg, int, fd, struct mmsghdr __user *, mmsg,
		unsigned int, vlen, unsigned int, flags,
		struct timespec __user *, timeout)

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