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| author | Jiri Bohac <jbohac@suse.cz> | 2016-10-20 12:29:26 +0200 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2016-10-20 14:29:11 -0400 |
| commit | 7aa8e63f0d0f2e0ae353632bca1ce75a258696c6 (patch) | |
| tree | 296d579460ec8de98617fd4c63945f4cf4db2aae /net/ipv6/addrconf.c | |
| parent | 8be0328e52dc2c8c6f61563c9ccc95ae4d63e9ce (diff) | |
| download | lwn-7aa8e63f0d0f2e0ae353632bca1ce75a258696c6.tar.gz lwn-7aa8e63f0d0f2e0ae353632bca1ce75a258696c6.zip | |
ipv6: properly prevent temp_prefered_lft sysctl race
The check for an underflow of tmp_prefered_lft is always false
because tmp_prefered_lft is unsigned. The intention of the check
was to guard against racing with an update of the
temp_prefered_lft sysctl, potentially resulting in an underflow.
As suggested by David Miller, the best way to prevent the race is
by reading the sysctl variable using READ_ONCE.
Signed-off-by: Jiri Bohac <jbohac@suse.cz>
Reported-by: Julia Lawall <julia.lawall@lip6.fr>
Fixes: 76506a986dc3 ("IPv6: fix DESYNC_FACTOR")
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/ipv6/addrconf.c')
| -rw-r--r-- | net/ipv6/addrconf.c | 9 |
1 files changed, 4 insertions, 5 deletions
diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c index cc7c26d05f45..060dd9922018 100644 --- a/net/ipv6/addrconf.c +++ b/net/ipv6/addrconf.c @@ -1185,6 +1185,7 @@ static int ipv6_create_tempaddr(struct inet6_ifaddr *ifp, struct inet6_ifaddr *i u32 addr_flags; unsigned long now = jiffies; long max_desync_factor; + s32 cnf_temp_preferred_lft; write_lock_bh(&idev->lock); if (ift) { @@ -1228,9 +1229,10 @@ retry: /* recalculate max_desync_factor each time and update * idev->desync_factor if it's larger */ + cnf_temp_preferred_lft = READ_ONCE(idev->cnf.temp_prefered_lft); max_desync_factor = min_t(__u32, idev->cnf.max_desync_factor, - idev->cnf.temp_prefered_lft - regen_advance); + cnf_temp_preferred_lft - regen_advance); if (unlikely(idev->desync_factor > max_desync_factor)) { if (max_desync_factor > 0) { @@ -1245,11 +1247,8 @@ retry: tmp_valid_lft = min_t(__u32, ifp->valid_lft, idev->cnf.temp_valid_lft + age); - tmp_prefered_lft = idev->cnf.temp_prefered_lft + age - + tmp_prefered_lft = cnf_temp_preferred_lft + age - idev->desync_factor; - /* guard against underflow in case of concurrent updates to cnf */ - if (unlikely(tmp_prefered_lft < 0)) - tmp_prefered_lft = 0; tmp_prefered_lft = min_t(__u32, ifp->prefered_lft, tmp_prefered_lft); tmp_plen = ifp->prefix_len; tmp_tstamp = ifp->tstamp; |