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Subject[PATCH] [93/99] ipv6/udp: Use the correct variable to determine non-blocking condition
Date
2.6.35-longterm review patch.  If anyone has any objections, please let me know.

------------------
From: Xufeng Zhang <xufeng.zhang@windriver.com>

[ Upstream commit 32c90254ed4a0c698caa0794ebb4de63fcc69631 ]

udpv6_recvmsg() function is not using the correct variable to determine
whether or not the socket is in non-blocking operation, this will lead
to unexpected behavior when a UDP checksum error occurs.

Consider a non-blocking udp receive scenario: when udpv6_recvmsg() is
called by sock_common_recvmsg(), MSG_DONTWAIT bit of flags variable in
udpv6_recvmsg() is cleared by "flags & ~MSG_DONTWAIT" in this call:

err = sk->sk_prot->recvmsg(iocb, sk, msg, size, flags & MSG_DONTWAIT,
flags & ~MSG_DONTWAIT, &addr_len);

i.e. with udpv6_recvmsg() getting these values:

int noblock = flags & MSG_DONTWAIT
int flags = flags & ~MSG_DONTWAIT

So, when udp checksum error occurs, the execution will go to
csum_copy_err, and then the problem happens:

csum_copy_err:
...............
if (flags & MSG_DONTWAIT)
return -EAGAIN;
goto try_again;
...............
But it will always go to try_again as MSG_DONTWAIT has been cleared
from flags at call time -- only noblock contains the original value
of MSG_DONTWAIT, so the test should be:

if (noblock)
return -EAGAIN;
This is also consistent with what the ipv4/udp code does.

Signed-off-by: Xufeng Zhang <xufeng.zhang@windriver.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Andi Kleen <ak@linux.intel.com>

---
net/ipv6/udp.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
Index: linux-2.6.35.y/net/ipv6/udp.c
===================================================================
--- linux-2.6.35.y.orig/net/ipv6/udp.c
+++ linux-2.6.35.y/net/ipv6/udp.c
@@ -445,7 +445,7 @@ csum_copy_err:
}
unlock_sock_fast(sk, slow);

- if (flags & MSG_DONTWAIT)
+ if (noblock)
return -EAGAIN;
goto try_again;
}

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