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authorDaniel Borkmann <daniel@iogearbox.net>2016-09-08 01:03:42 +0200
committerDavid S. Miller <davem@davemloft.net>2016-09-09 02:28:37 +0200
commit2d2be8cab26ed918e94d2deae89580003242a123 (patch)
tree78371d83d8f4f43a4c24268b93bbbbcb3813d901 /sound
parenttcp: use an RB tree for ooo receive queue (diff)
downloadlinux-2d2be8cab26ed918e94d2deae89580003242a123.tar.xz
linux-2d2be8cab26ed918e94d2deae89580003242a123.zip
bpf: fix range propagation on direct packet access
LLVM can generate code that tests for direct packet access via skb->data/data_end in a way that currently gets rejected by the verifier, example: [...] 7: (61) r3 = *(u32 *)(r6 +80) 8: (61) r9 = *(u32 *)(r6 +76) 9: (bf) r2 = r9 10: (07) r2 += 54 11: (3d) if r3 >= r2 goto pc+12 R1=inv R2=pkt(id=0,off=54,r=0) R3=pkt_end R4=inv R6=ctx R9=pkt(id=0,off=0,r=0) R10=fp 12: (18) r4 = 0xffffff7a 14: (05) goto pc+430 [...] from 11 to 24: R1=inv R2=pkt(id=0,off=54,r=0) R3=pkt_end R4=inv R6=ctx R9=pkt(id=0,off=0,r=0) R10=fp 24: (7b) *(u64 *)(r10 -40) = r1 25: (b7) r1 = 0 26: (63) *(u32 *)(r6 +56) = r1 27: (b7) r2 = 40 28: (71) r8 = *(u8 *)(r9 +20) invalid access to packet, off=20 size=1, R9(id=0,off=0,r=0) The reason why this gets rejected despite a proper test is that we currently call find_good_pkt_pointers() only in case where we detect tests like rX > pkt_end, where rX is of type pkt(id=Y,off=Z,r=0) and derived, for example, from a register of type pkt(id=Y,off=0,r=0) pointing to skb->data. find_good_pkt_pointers() then fills the range in the current branch to pkt(id=Y,off=0,r=Z) on success. For above case, we need to extend that to recognize pkt_end >= rX pattern and mark the other branch that is taken on success with the appropriate pkt(id=Y,off=0,r=Z) type via find_good_pkt_pointers(). Since eBPF operates on BPF_JGT (>) and BPF_JGE (>=), these are the only two practical options to test for from what LLVM could have generated, since there's no such thing as BPF_JLT (<) or BPF_JLE (<=) that we would need to take into account as well. After the fix: [...] 7: (61) r3 = *(u32 *)(r6 +80) 8: (61) r9 = *(u32 *)(r6 +76) 9: (bf) r2 = r9 10: (07) r2 += 54 11: (3d) if r3 >= r2 goto pc+12 R1=inv R2=pkt(id=0,off=54,r=0) R3=pkt_end R4=inv R6=ctx R9=pkt(id=0,off=0,r=0) R10=fp 12: (18) r4 = 0xffffff7a 14: (05) goto pc+430 [...] from 11 to 24: R1=inv R2=pkt(id=0,off=54,r=54) R3=pkt_end R4=inv R6=ctx R9=pkt(id=0,off=0,r=54) R10=fp 24: (7b) *(u64 *)(r10 -40) = r1 25: (b7) r1 = 0 26: (63) *(u32 *)(r6 +56) = r1 27: (b7) r2 = 40 28: (71) r8 = *(u8 *)(r9 +20) 29: (bf) r1 = r8 30: (25) if r8 > 0x3c goto pc+47 R1=inv56 R2=imm40 R3=pkt_end R4=inv R6=ctx R8=inv56 R9=pkt(id=0,off=0,r=54) R10=fp 31: (b7) r1 = 1 [...] Verifier test cases are also added in this work, one that demonstrates the mentioned example here and one that tries a bad packet access for the current/fall-through branch (the one with types pkt(id=X,off=Y,r=0), pkt(id=X,off=0,r=0)), then a case with good and bad accesses, and two with both test variants (>, >=). Fixes: 969bf05eb3ce ("bpf: direct packet access") Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'sound')
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