In most places that write files to the object database (even packfiles via index-pack or fast-import), we use finalize_object_file(). This prefers link()/unlink() over rename(), because it means we will prefer data that is already in the repository to data that we are newly writing. We should do the same thing in pack-objects. Even though we don't think of it as accepting outside data (and thus not being susceptible to collision attacks), in theory a determined attacker could present just the right set of objects to cause an incremental repack to generate a pack with their desired hash. This has some test and real-world fallout, as seen in the adjustment to t5303 below. That test script assumes that we can "fix" corruption by repacking into a good state, including when the pack generated by that repack operation collides with a (corrupted) pack with the same hash. This violates our assumption from the previous adjustments to finalize_object_file() that if we're moving a new file over an existing one, that since their checksums match, so too must their contents. This makes "fixing" corruption like this a more explicit operation, since the test (and users, who may fix real-life corruption using a similar technique) must first move the broken contents out of the way. Note also that we now call adjust_shared_perm() twice. We already call adjust_shared_perm() in stage_tmp_packfiles(), and now call it again in finalize_object_file(). This is somewhat wasteful, but cleaning up the existing calls to adjust_shared_perm() is tricky (because sometimes we're writing to a tmpfile, and sometimes we're writing directly into the final destination), so let's tolerate some minor waste until we can more carefully clean up the now-redundant calls. Co-authored-by: Jeff King <peff@xxxxxxxx> Signed-off-by: Jeff King <peff@xxxxxxxx> Signed-off-by: Taylor Blau <me@xxxxxxxxxxxx> --- pack-write.c | 7 ++++--- t/t5303-pack-corruption-resilience.sh | 7 ++++++- 2 files changed, 10 insertions(+), 4 deletions(-) diff --git a/pack-write.c b/pack-write.c index 27965672f1..f415604c15 100644 --- a/pack-write.c +++ b/pack-write.c @@ -8,6 +8,7 @@ #include "csum-file.h" #include "remote.h" #include "chunk-format.h" +#include "object-file.h" #include "pack-mtimes.h" #include "pack-objects.h" #include "pack-revindex.h" @@ -528,9 +529,9 @@ static void rename_tmp_packfile(struct strbuf *name_prefix, const char *source, size_t name_prefix_len = name_prefix->len; strbuf_addstr(name_prefix, ext); - if (rename(source, name_prefix->buf)) - die_errno("unable to rename temporary file to '%s'", - name_prefix->buf); + if (finalize_object_file(source, name_prefix->buf)) + die("unable to rename temporary file to '%s'", + name_prefix->buf); strbuf_setlen(name_prefix, name_prefix_len); } diff --git a/t/t5303-pack-corruption-resilience.sh b/t/t5303-pack-corruption-resilience.sh index 61469ef4a6..e6a43ec9ae 100755 --- a/t/t5303-pack-corruption-resilience.sh +++ b/t/t5303-pack-corruption-resilience.sh @@ -44,9 +44,14 @@ create_new_pack() { } do_repack() { + for f in $pack.* + do + mv $f "$(echo $f | sed -e 's/pack-/pack-corrupt-/')" || return 1 + done && pack=$(printf "$blob_1\n$blob_2\n$blob_3\n" | git pack-objects $@ .git/objects/pack/pack) && - pack=".git/objects/pack/pack-${pack}" + pack=".git/objects/pack/pack-${pack}" && + rm -f .git/objects/pack/pack-corrupt-* } do_corrupt_object() { -- 2.46.1.507.gffd0c9a15b2.dirty