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authorAlexei Starovoitov <ast@fb.com>2016-05-19 18:17:13 -0700
committerDavid S. Miller <davem@davemloft.net>2016-05-20 19:53:03 -0400
commitd91b28ed42de99217efb2e8cb0357263d6fb737c (patch)
treeb75e365810041e821fbcfe0824e18aef0e36820e /kernel/bpf
parent238a9584e9e2c7b3ea23924e9183fee05d584789 (diff)
downloadlinux-sh-d91b28ed42de99217efb2e8cb0357263d6fb737c.tar.gz
bpf: support decreasing order in direct packet access
when packet headers are accessed in 'decreasing' order (like TCP port may be fetched before the program reads IP src) the llvm may generate the following code: [...] // R7=pkt(id=0,off=22,r=70) r2 = *(u32 *)(r7 +0) // good access [...] r7 += 40 // R7=pkt(id=0,off=62,r=70) r8 = *(u32 *)(r7 +0) // good access [...] r1 = *(u32 *)(r7 -20) // this one will fail though it's within a safe range // it's doing *(u32*)(skb->data + 42) Fix verifier to recognize such code pattern Alos turned out that 'off > range' condition is not a verifier bug. It's a buggy program that may do something like: if (ptr + 50 > data_end) return 0; ptr += 60; *(u32*)ptr; in such case emit "invalid access to packet, off=0 size=4, R1(id=0,off=60,r=50)" error message, so all information is available for the program author to fix the program. Fixes: 969bf05eb3ce ("bpf: direct packet access") Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'kernel/bpf')
-rw-r--r--kernel/bpf/verifier.c12
1 files changed, 4 insertions, 8 deletions
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index a08d66215245..d54e34874579 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -683,15 +683,11 @@ static int check_packet_access(struct verifier_env *env, u32 regno, int off,
{
struct reg_state *regs = env->cur_state.regs;
struct reg_state *reg = &regs[regno];
- int linear_size = (int) reg->range - (int) reg->off;
- if (linear_size < 0 || linear_size >= MAX_PACKET_OFF) {
- verbose("verifier bug\n");
- return -EFAULT;
- }
- if (off < 0 || off + size > linear_size) {
- verbose("invalid access to packet, off=%d size=%d, allowed=%d\n",
- off, size, linear_size);
+ off += reg->off;
+ if (off < 0 || off + size > reg->range) {
+ verbose("invalid access to packet, off=%d size=%d, R%d(id=%d,off=%d,r=%d)\n",
+ off, size, regno, reg->id, reg->off, reg->range);
return -EACCES;
}
return 0;