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authorGreg Kurz <groug@kaod.org>2018-04-05 16:19:44 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2018-04-05 21:36:22 -0700
commita85222435bd055b2d2cedc515d810a5ea6c05432 (patch)
tree5cb9623e7cdb4229ab9bd90d559d5a6d895aa1fc /net/9p/client.c
parentde37428638ec7d22b46c4c20b8536f3681559e2c (diff)
net/9p: avoid -ERESTARTSYS leak to userspace
If it was interrupted by a signal, the 9p client may need to send some more requests to the server for cleanup before returning to userspace. To avoid such a last minute request to be interrupted right away, the client memorizes if a signal is pending, clears TIF_SIGPENDING, handles the request and calls recalc_sigpending() before returning. Unfortunately, if the transmission of this cleanup request fails for any reason, the transport returns an error and the client propagates it right away, without calling recalc_sigpending(). This ends up with -ERESTARTSYS from the initially interrupted request crawling up to syscall exit, with TIF_SIGPENDING cleared by the cleanup request. The specific signal handling code, which is responsible for converting -ERESTARTSYS to -EINTR is not called, and userspace receives the confusing errno value: open: Unknown error 512 (512) This is really hard to hit in real life. I discovered the issue while working on hot-unplug of a virtio-9p-pci device with an instrumented QEMU allowing to control request completion. Both p9_client_zc_rpc() and p9_client_rpc() functions have this buggy error path actually. Their code flow is a bit obscure and the best thing to do would probably be a full rewrite: to really ensure this situation of clearing TIF_SIGPENDING and returning -ERESTARTSYS can never happen. But given the general lack of interest for the 9p code, I won't risk breaking more things. So this patch simply fixes the buggy paths in both functions with a trivial label+goto. Thanks to Laurent Dufour for his help and suggestions on how to find the root cause and how to fix it. Link: http://lkml.kernel.org/r/152062809886.10599.7361006774123053312.stgit@bahia.lan Signed-off-by: Greg Kurz <groug@kaod.org> Reviewed-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Yiwen Jiang <jiangyiwen@huawei.com> Cc: Eric Van Hensbergen <ericvh@gmail.com> Cc: Ron Minnich <rminnich@sandia.gov> Cc: Latchesar Ionkov <lucho@ionkov.net> Cc: David Miller <davem@davemloft.net> Cc: Laurent Dufour <ldufour@linux.vnet.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'net/9p/client.c')
-rw-r--r--net/9p/client.c6
1 files changed, 4 insertions, 2 deletions
diff --git a/net/9p/client.c b/net/9p/client.c
index b433aff5ff13..e6cae8332e2e 100644
--- a/net/9p/client.c
+++ b/net/9p/client.c
@@ -769,7 +769,7 @@ p9_client_rpc(struct p9_client *c, int8_t type, const char *fmt, ...)
if (err < 0) {
if (err != -ERESTARTSYS && err != -EFAULT)
c->status = Disconnected;
- goto reterr;
+ goto recalc_sigpending;
}
again:
/* Wait for the response */
@@ -804,6 +804,7 @@ again:
if (req->status == REQ_STATUS_RCVD)
err = 0;
}
+recalc_sigpending:
if (sigpending) {
spin_lock_irqsave(&current->sighand->siglock, flags);
recalc_sigpending();
@@ -867,7 +868,7 @@ static struct p9_req_t *p9_client_zc_rpc(struct p9_client *c, int8_t type,
if (err == -EIO)
c->status = Disconnected;
if (err != -ERESTARTSYS)
- goto reterr;
+ goto recalc_sigpending;
}
if (req->status == REQ_STATUS_ERROR) {
p9_debug(P9_DEBUG_ERROR, "req_status error %d\n", req->t_err);
@@ -885,6 +886,7 @@ static struct p9_req_t *p9_client_zc_rpc(struct p9_client *c, int8_t type,
if (req->status == REQ_STATUS_RCVD)
err = 0;
}
+recalc_sigpending:
if (sigpending) {
spin_lock_irqsave(&current->sighand->siglock, flags);
recalc_sigpending();