net: ipv4: emulate READ_ONCE() on ->hdrincl bit-field in raw_sendmsg()
Commit 8f659a03 ("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: 8f659a03 ("net: ipv4: fix for a race condition in raw_sendmsg") Signed-off-by: NNicolai Stange <nstange@suse.de> Reviewed-by: NStefano Brivio <sbrivio@redhat.com> Signed-off-by: NDavid S. Miller <davem@davemloft.net>
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