From 34b88a68f26a75e4fded796f1a49c40f82234b7d Mon Sep 17 00:00:00 2001 From: Arnaldo Carvalho de Melo Date: Mon, 14 Mar 2016 09:56:35 -0300 Subject: [PATCH] net: Fix use after free in the recvmmsg exit path The syzkaller fuzzer hit the following use-after-free: Call Trace: [] __asan_report_load8_noabort+0x3e/0x40 mm/kasan/report.c:295 [] __sys_recvmmsg+0x6fa/0x7f0 net/socket.c:2261 [< inline >] SYSC_recvmmsg net/socket.c:2281 [] SyS_recvmmsg+0x16f/0x180 net/socket.c:2270 [] 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 Cc: Alexander Potapenko Cc: Eric Dumazet Cc: Kostya Serebryany Cc: Sasha Levin Fixes: a2e2725541fa ("net: Introduce recvmmsg socket syscall") http://lkml.kernel.org/r/20160122211644.GC2470@redhat.com Signed-off-by: Arnaldo Carvalho de Melo Signed-off-by: David S. Miller --- net/socket.c | 44 ++++++++++++++++++++++---------------------- 1 file changed, 22 insertions(+), 22 deletions(-) diff --git a/net/socket.c b/net/socket.c index c5ddc52cf2b2..5f77a8e93830 100644 --- a/net/socket.c +++ b/net/socket.c @@ -2244,31 +2244,31 @@ int __sys_recvmmsg(int fd, struct mmsghdr __user *mmsg, unsigned int vlen, cond_resched(); } + if (err == 0) + goto out_put; + + if (datagrams == 0) { + datagrams = err; + goto out_put; + } + + /* + * We may return less entries than requested (vlen) if the + * sock is non block and there aren't enough datagrams... + */ + if (err != -EAGAIN) { + /* + * ... or if recvmsg returns an error after we + * received some datagrams, where we record the + * error to return on the next call or if the + * app asks about it using getsockopt(SO_ERROR). + */ + sock->sk->sk_err = -err; + } out_put: fput_light(sock->file, fput_needed); - if (err == 0) - return datagrams; - - if (datagrams != 0) { - /* - * We may return less entries than requested (vlen) if the - * sock is non block and there aren't enough datagrams... - */ - if (err != -EAGAIN) { - /* - * ... or if recvmsg returns an error after we - * received some datagrams, where we record the - * error to return on the next call or if the - * app asks about it using getsockopt(SO_ERROR). - */ - sock->sk->sk_err = -err; - } - - return datagrams; - } - - return err; + return datagrams; } SYSCALL_DEFINE5(recvmmsg, int, fd, struct mmsghdr __user *, mmsg,