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>
Cc: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
1 file changed