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netfilter: conntrack: fix race between nf_conntrack proc read and has…
…h resize When we do "cat /proc/net/nf_conntrack", and meanwhile resize the conntrack hash table via /sys/module/nf_conntrack/parameters/hashsize, race will happen, because reader can observe a newly allocated hash but the old size (or vice versa). So oops will happen like follows: BUG: unable to handle kernel NULL pointer dereference at 0000000000000017 IP: [<ffffffffa0418e21>] seq_print_acct+0x11/0x50 [nf_conntrack] Call Trace: [<ffffffffa0412f4e>] ? ct_seq_show+0x14e/0x340 [nf_conntrack] [<ffffffff81261a1c>] seq_read+0x2cc/0x390 [<ffffffff812a8d62>] proc_reg_read+0x42/0x70 [<ffffffff8123bee7>] __vfs_read+0x37/0x130 [<ffffffff81347980>] ? security_file_permission+0xa0/0xc0 [<ffffffff8123cf75>] vfs_read+0x95/0x140 [<ffffffff8123e475>] SyS_read+0x55/0xc0 [<ffffffff817c2572>] entry_SYSCALL_64_fastpath+0x1a/0xa4 It is very easy to reproduce this kernel crash. 1. open one shell and input the following cmds: while : ; do echo $RANDOM > /sys/module/nf_conntrack/parameters/hashsize done 2. open more shells and input the following cmds: while : ; do cat /proc/net/nf_conntrack done 3. just wait a monent, oops will happen soon. The solution in this patch is based on Florian's Commit 5e3c61f ("netfilter: conntrack: fix lookup race during hash resize"). And add a wrapper function nf_conntrack_get_ht to get hash and hsize suggested by Florian Westphal. Signed-off-by: Liping Zhang <liping.zhang@spreadtrum.com> Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
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Liping Zhang
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Pablo Neira Ayuso
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Jul 11, 2016
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