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author | Greg Kurz <groug@kaod.org> | 2018-04-05 16:19:44 -0700 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2018-04-05 21:36:22 -0700 |
commit | a85222435bd055b2d2cedc515d810a5ea6c05432 (patch) | |
tree | 5cb9623e7cdb4229ab9bd90d559d5a6d895aa1fc /net/9p/client.c | |
parent | de37428638ec7d22b46c4c20b8536f3681559e2c (diff) | |
download | linux-stable-a85222435bd055b2d2cedc515d810a5ea6c05432.tar.gz linux-stable-a85222435bd055b2d2cedc515d810a5ea6c05432.tar.bz2 linux-stable-a85222435bd055b2d2cedc515d810a5ea6c05432.zip |
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.c | 6 |
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(¤t->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(¤t->sighand->siglock, flags); recalc_sigpending(); |