Revision c6a9efa1d8353d8960d152e7d469d952b01495c0 authored by Paul Chaignon on 24 April 2019, 19:50:42 UTC, committed by Alexei Starovoitov on 26 April 2019, 00:20:06 UTC
In case of a null check on a pointer inside a subprog, we should mark all registers with this pointer as either safe or unknown, in both the current and previous frames. Currently, only spilled registers and registers in the current frame are marked. Packet bound checks in subprogs have the same issue. This patch fixes it to mark registers in previous frames as well. A good reproducer for null checks looks as follow: 1: ptr = bpf_map_lookup_elem(map, &key); 2: ret = subprog(ptr) { 3: return ptr != NULL; 4: } 5: if (ret) 6: value = *ptr; With the above, the verifier will complain on line 6 because it sees ptr as map_value_or_null despite the null check in subprog 1. Note that this patch fixes another resulting bug when using bpf_sk_release(): 1: sk = bpf_sk_lookup_tcp(...); 2: subprog(sk) { 3: if (sk) 4: bpf_sk_release(sk); 5: } 6: if (!sk) 7: return 0; 8: return 1; In the above, mark_ptr_or_null_regs will warn on line 6 because it will try to free the reference state, even though it was already freed on line 3. Fixes: f4d7e40a5b71 ("bpf: introduce function calls (verification)") Signed-off-by: Paul Chaignon <paul.chaignon@orange.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org>
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