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authorNicolai Stange <nstange@suse.de>2018-01-08 15:54:44 +0100
committerDavid S. Miller <davem@davemloft.net>2018-01-09 11:59:16 -0500
commit20b50d79974ea3192e8c3ab7faf4e536e5f14d8f (patch)
treec25a3de78f24e225e238e1ffe3eebb193f5da3f0 /net
parent3dc2fa47549aca71773afdd12a78d31802bb22b4 (diff)
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net: ipv4: emulate READ_ONCE() on ->hdrincl bit-field in raw_sendmsg()
Commit 8f659a03a0ba ("net: ipv4: fix for a race condition in raw_sendmsg") fixed the issue of possibly inconsistent ->hdrincl handling due to concurrent updates by reading this bit-field member into a local variable and using the thus stabilized value in subsequent tests. However, aforementioned commit also adds the (correct) comment that /* hdrincl should be READ_ONCE(inet->hdrincl) * but READ_ONCE() doesn't work with bit fields */ because as it stands, the compiler is free to shortcut or even eliminate the local variable at its will. Note that I have not seen anything like this happening in reality and thus, the concern is a theoretical one. However, in order to be on the safe side, emulate a READ_ONCE() on the bit-field by doing it on the local 'hdrincl' variable itself: int hdrincl = inet->hdrincl; hdrincl = READ_ONCE(hdrincl); This breaks the chain in the sense that the compiler is not allowed to replace subsequent reads from hdrincl with reloads from inet->hdrincl. Fixes: 8f659a03a0ba ("net: ipv4: fix for a race condition in raw_sendmsg") Signed-off-by: Nicolai Stange <nstange@suse.de> Reviewed-by: Stefano Brivio <sbrivio@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net')
-rw-r--r--net/ipv4/raw.c4
1 files changed, 3 insertions, 1 deletions
diff --git a/net/ipv4/raw.c b/net/ipv4/raw.c
index 125c1eab3eaa..5e570aa9e43b 100644
--- a/net/ipv4/raw.c
+++ b/net/ipv4/raw.c
@@ -520,9 +520,11 @@ static int raw_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
goto out;
/* hdrincl should be READ_ONCE(inet->hdrincl)
- * but READ_ONCE() doesn't work with bit fields
+ * but READ_ONCE() doesn't work with bit fields.
+ * Doing this indirectly yields the same result.
*/
hdrincl = inet->hdrincl;
+ hdrincl = READ_ONCE(hdrincl);
/*
* Check the flags.
*/