bpf: tail calls do not modify packet data #6245
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The bpf verifier checks whether packet data is modified within a helper function, and if so invalidates the pointer to that data. Currently the verifier always invalidates if the helper function called is a tail call, as it cannot tell whether the called function does or does not modify the packet data. However, in this case, the fact that the packet might be modified is irrelevant in the code following the helper call, as the tail call only returns if there is nothing to execute, otherwise the calling (sub)program will return directly after the tail call finished. So it is this (sub)program for which the pointer to packet data needs to be invalidated. Fortunately, there are already two distinct points in the code for invalidating packet pointers directly after a helper call, and for entire (sub)programs. This commit assures that the pointer is only invalidated in the relevant case. Note that this is a regression bug: taking care of tail calls only became necessary when subprograms were introduced, before commit 1a4607f using a packet pointer after a tail call was working fine, as it should. Fixes: 1a4607f ("bpf: consider that tail calls invalidate packet pointers") Signed-off-by: Martin Teichmann <[email protected]>
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Upstream branch: 2cbb259 |
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Pull request for series with
subject: bpf: tail calls do not modify packet data
version: 1
url: https://patchwork.kernel.org/project/netdevbpf/list/?series=1017201