4.2.8-ckt7 -stable review patch. If anyone has any objections, please let me know.
---8<------------------------------------------------------------ From: Arnaldo Carvalho de Melo <[email protected]> commit 34b88a68f26a75e4fded796f1a49c40f82234b7d upstream. 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 <[email protected]> Cc: Alexander Potapenko <[email protected]> Cc: Eric Dumazet <[email protected]> Cc: Kostya Serebryany <[email protected]> Cc: Sasha Levin <[email protected]> Fixes: a2e2725541fa ("net: Introduce recvmmsg socket syscall") http://lkml.kernel.org/r/[email protected] Signed-off-by: Arnaldo Carvalho de Melo <[email protected]> Signed-off-by: David S. Miller <[email protected]> Signed-off-by: Kamal Mostafa <[email protected]> --- net/socket.c | 38 +++++++++++++++++++------------------- 1 file changed, 19 insertions(+), 19 deletions(-) diff --git a/net/socket.c b/net/socket.c index f3fbe17..f20cd74 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, break; } -out_put: - fput_light(sock->file, fput_needed); - if (err == 0) - return datagrams; + goto out_put; - if (datagrams != 0) { + 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) { /* - * We may return less entries than requested (vlen) if the - * sock is non block and there aren't enough datagrams... + * ... 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). */ - 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; + sock->sk->sk_err = -err; } +out_put: + fput_light(sock->file, fput_needed); - return err; + return datagrams; } SYSCALL_DEFINE5(recvmmsg, int, fd, struct mmsghdr __user *, mmsg, -- 2.7.4
