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smart_pkt: verify packet length exceeds PKT_LEN_SIZE

Each packet line in the Git protocol is prefixed by a four-byte
length of how much data will follow, which we parse in
`git_pkt_parse_line`. The transmitted length can either be equal
to zero in case of a flush packet or has to be at least of length
four, as it also includes the encoded length itself. Not
checking this may result in a buffer overflow as we directly pass
the length to functions which accept a `size_t` length as
parameter.

Fix the issue by verifying that non-flush packets have at least a
length of `PKT_LEN_SIZE`.
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pks-t authored and ethomson committed Nov 15, 2016
1 parent 75db289 commit 66e3774d279672ee51c3b54545a79d20d1ada834
Showing with 8 additions and 0 deletions.
  1. +8 −0 src/transports/smart_pkt.c
@@ -427,6 +427,14 @@ int git_pkt_parse_line(
if (bufflen > 0 && bufflen < (size_t)len)
return GIT_EBUFS;

/*
* The length has to be exactly 0 in case of a flush
* packet or greater than PKT_LEN_SIZE, as the decoded
* length includes its own encoded length of four bytes.
*/
if (len != 0 && len < PKT_LEN_SIZE)
return GIT_ERROR;

line += PKT_LEN_SIZE;
/*
* TODO: How do we deal with empty lines? Try again? with the next

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