3.16.75-rc1 review patch. If anyone has any objections, please let me know.
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From: WANG Cong xiyou.wangcong@gmail.com
commit c38b7d327aafd1e3ad7ff53eefac990673b65667 upstream.
Andrey reported a use-after-free in add_grec():
for (psf = *psf_list; psf; psf = psf_next) { ... psf_next = psf->sf_next;
where the struct ip_sf_list's were already freed by:
kfree+0xe8/0x2b0 mm/slub.c:3882 ip_mc_clear_src+0x69/0x1c0 net/ipv4/igmp.c:2078 ip_mc_dec_group+0x19a/0x470 net/ipv4/igmp.c:1618 ip_mc_drop_socket+0x145/0x230 net/ipv4/igmp.c:2609 inet_release+0x4e/0x1c0 net/ipv4/af_inet.c:411 sock_release+0x8d/0x1e0 net/socket.c:597 sock_close+0x16/0x20 net/socket.c:1072
This happens because we don't hold pmc->lock in ip_mc_clear_src() and a parallel mr_ifc_timer timer could jump in and access them.
The RCU lock is there but it is merely for pmc itself, this spinlock could actually ensure we don't access them in parallel.
Thanks to Eric and Long for discussion on this bug.
Reported-by: Andrey Konovalov andreyknvl@google.com Cc: Eric Dumazet edumazet@google.com Cc: Xin Long lucien.xin@gmail.com Signed-off-by: Cong Wang xiyou.wangcong@gmail.com Reviewed-by: Xin Long lucien.xin@gmail.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Ben Hutchings ben@decadent.org.uk --- net/ipv4/igmp.c | 21 +++++++++++++-------- 1 file changed, 13 insertions(+), 8 deletions(-)
--- a/net/ipv4/igmp.c +++ b/net/ipv4/igmp.c @@ -1880,21 +1880,26 @@ static int ip_mc_add_src(struct in_devic
static void ip_mc_clear_src(struct ip_mc_list *pmc) { - struct ip_sf_list *psf, *nextpsf; + struct ip_sf_list *psf, *nextpsf, *tomb, *sources;
- for (psf = pmc->tomb; psf; psf = nextpsf) { + spin_lock_bh(&pmc->lock); + tomb = pmc->tomb; + pmc->tomb = NULL; + sources = pmc->sources; + pmc->sources = NULL; + pmc->sfmode = MCAST_EXCLUDE; + pmc->sfcount[MCAST_INCLUDE] = 0; + pmc->sfcount[MCAST_EXCLUDE] = 1; + spin_unlock_bh(&pmc->lock); + + for (psf = tomb; psf; psf = nextpsf) { nextpsf = psf->sf_next; kfree(psf); } - pmc->tomb = NULL; - for (psf = pmc->sources; psf; psf = nextpsf) { + for (psf = sources; psf; psf = nextpsf) { nextpsf = psf->sf_next; kfree(psf); } - pmc->sources = NULL; - pmc->sfmode = MCAST_EXCLUDE; - pmc->sfcount[MCAST_INCLUDE] = 0; - pmc->sfcount[MCAST_EXCLUDE] = 1; }