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revlog: detect incomplete revlog reads

Authored by indygreg on Nov 13 2018, 3:41 PM.



_readsegment() is supposed to return N bytes of revlog revision
data starting at a file offset. Surprisingly, its behavior before
this patch never verified that it actually read and returned N
bytes! Instead, it would perform the read(), then return whatever
data was available. And even more surprisingly, nothing in the
call chain appears to have been validating that it received all
the data it was expecting.

This behavior could lead to partial or incomplete revision chunks
being operated on. This could result in e.g. cached deltas being
applied against incomplete base revisions. The delta application
process would happily perform this operation. Only hash
verification would detect the corruption and save us.

This commit changes the behavior of raw revlog reading to validate
that we actually read() the number of bytes that were requested.
We will raise a more specific error faster, rather than possibly
have it go undetected or manifest later in the call stack, at
delta application or hash verification.

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rHG Mercurial
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Automatic diff as part of commit; unit tests not applicable.

Event Timeline

indygreg created this revision.Nov 13 2018, 3:41 PM
This revision was automatically updated to reflect the committed changes.