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netfilter: ebtables: reject blobs that don't provide all entry points
Harshit Mogalapalli says: In ebt_do_table() function dereferencing 'private->hook_entry[hook]' can lead to NULL pointer dereference. [..] Kernel panic: general protection fault, probably for non-canonical address 0xdffffc0000000005: 0000 [#1] PREEMPT SMP KASAN KASAN: null-ptr-deref in range [0x0000000000000028-0x000000000000002f] [..] RIP: 0010:ebt_do_table+0x1dc/0x1ce0 Code: 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 5c 16 00 00 48 b8 00 00 00 00 00 fc ff df 49 8b 6c df 08 48 8d 7d 2c 48 89 fa 48 c1 ea 03 <0f> b6 14 02 48 89 f8 83 e0 07 83 c0 03 38 d0 7c 08 84 d2 0f 85 88 [..] Call Trace: nf_hook_slow+0xb1/0x170 __br_forward+0x289/0x730 maybe_deliver+0x24b/0x380 br_flood+0xc6/0x390 br_dev_xmit+0xa2e/0x12c0 For some reason ebtables rejects blobs that provide entry points that are not supported by the table, but what it should instead reject is the opposite: blobs that DO NOT provide an entry point supported by the table. t->valid_hooks is the bitmask of hooks (input, forward ...) that will see packets. Providing an entry point that is not support is harmless (never called/used), but the inverse isn't: it results in a crash because the ebtables traverser doesn't expect a NULL blob for a location its receiving packets for. Instead of fixing all the individual checks, do what iptables is doing and reject all blobs that differ from the expected hooks. Fixes: 1da177e ("Linux-2.6.12-rc2") Reported-by: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com> Reported-by: syzkaller <syzkaller@googlegroups.com> Signed-off-by: Florian Westphal <fw@strlen.de>
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Florian Westphal
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