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net: ipv4: emulate READ_ONCE() on ->hdrincl bit-field in raw_sendmsg()
Commit8f659a03a0
("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:8f659a03a0
("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>
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1 changed files with 3 additions and 1 deletions
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@ -520,9 +520,11 @@ static int raw_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
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goto out;
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/* hdrincl should be READ_ONCE(inet->hdrincl)
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* but READ_ONCE() doesn't work with bit fields
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* but READ_ONCE() doesn't work with bit fields.
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* Doing this indirectly yields the same result.
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*/
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hdrincl = inet->hdrincl;
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hdrincl = READ_ONCE(hdrincl);
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/*
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* Check the flags.
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*/
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