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| author | Nicolai Stange <nstange@suse.de> | 2018-01-08 15:54:44 +0100 |
|---|---|---|
| committer | Ben Hutchings <ben@decadent.org.uk> | 2018-03-03 15:50:57 +0000 |
| commit | 56ff66d24079a470e430b751800b2c642d443e88 (patch) | |
| tree | b912ba583394994312b5bcb789dd05eba3844951 | |
| parent | d1168c13578d3b6645c41314c8e0ce0ee0c85f6a (diff) | |
| download | linux-56ff66d24079a470e430b751800b2c642d443e88.tar.gz linux-56ff66d24079a470e430b751800b2c642d443e88.tar.bz2 linux-56ff66d24079a470e430b751800b2c642d443e88.zip | |
net: ipv4: emulate READ_ONCE() on ->hdrincl bit-field in raw_sendmsg()
commit 20b50d79974ea3192e8c3ab7faf4e536e5f14d8f upstream.
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>
[bwh: Backported to 3.2: use ACCESS_ONCE()]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
| -rw-r--r-- | net/ipv4/raw.c | 4 |
1 files changed, 3 insertions, 1 deletions
diff --git a/net/ipv4/raw.c b/net/ipv4/raw.c index a02d3cdd05e0..8a9233ed322b 100644 --- a/net/ipv4/raw.c +++ b/net/ipv4/raw.c @@ -491,9 +491,11 @@ static int raw_sendmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg, 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 = ACCESS_ONCE(hdrincl); /* * Check the flags. */ |