sha1_file: Fix infinite loop when pack is corrupted

Some types of corruption to a pack may confuse the deflate stream
which stores an object.  In Andy's reported case a 36 byte region
of the pack was overwritten, leading to what appeared to be a valid
deflate stream that was trying to produce a result larger than our
allocated output buffer could accept.

Z_BUF_ERROR is returned from inflate() if either the input buffer
needs more input bytes, or the output buffer has run out of space.
Previously we only considered the former case, as it meant we needed
to move the stream's input buffer to the next window in the pack.

We now abort the loop if inflate() returns Z_BUF_ERROR without
consuming the entire input buffer it was given, or has filled
the entire output buffer but has not yet returned Z_STREAM_END.
Either state is a clear indicator that this loop is not working
as expected, and should not continue.

This problem cannot occur with loose objects as we open the entire
loose object as a single buffer and treat Z_BUF_ERROR as an error.

Reported-by: Andy Isaacson <adi@hexapodia.org>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Acked-by: Nicolas Pitre <nico@fluxnic.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/sha1_file.c b/sha1_file.c
index 4ea0b18d0aaeca48ed75ed21863195c5ce830cbc..4cc8939e4b901c1eda75a71705021c749c9a48b0 100644 (file)
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -1357,6 +1357,8 @@ unsigned long get_size_from_delta(struct packed_git *p,
                in = use_pack(p, w_curs, curpos, &stream.avail_in);
                stream.next_in = in;
                st = git_inflate(&stream, Z_FINISH);
+               if (st == Z_BUF_ERROR && (stream.avail_in || !stream.avail_out))
+                       break;
                curpos += stream.next_in - in;
        } while ((st == Z_OK || st == Z_BUF_ERROR) &&
                 stream.total_out < sizeof(delta_head));
@@ -1594,6 +1596,8 @@ static void *unpack_compressed_entry(struct packed_git *p,
                in = use_pack(p, w_curs, curpos, &stream.avail_in);
                stream.next_in = in;
                st = git_inflate(&stream, Z_FINISH);
+               if (st == Z_BUF_ERROR && (stream.avail_in || !stream.avail_out))
+                       break;
                curpos += stream.next_in - in;
        } while (st == Z_OK || st == Z_BUF_ERROR);
        git_inflate_end(&stream);

diff --git a/t/t5303-pack-corruption-resilience.sh b/t/t5303-pack-corruption-resilience.sh
index 5132d4130968691bb115f5fc08cd0d2fd64ce669..5f6cd4f3332f600888c402d2f1b72ddc8840b8cf 100755 (executable)
--- a/t/t5303-pack-corruption-resilience.sh
+++ b/t/t5303-pack-corruption-resilience.sh
@@ -275,4 +275,13 @@ test_expect_success \
      git cat-file blob $blob_2 > /dev/null &&
      git cat-file blob $blob_3 > /dev/null'
 
+test_expect_success \
+    'corrupting header to have too small output buffer fails unpack' \
+    'create_new_pack &&
+     git prune-packed &&
+     printf "\262\001" | do_corrupt_object $blob_1 0 &&
+     test_must_fail git cat-file blob $blob_1 > /dev/null &&
+     test_must_fail git cat-file blob $blob_2 > /dev/null &&
+     test_must_fail git cat-file blob $blob_3 > /dev/null'
+
 test_done