[PATCH 0/2] fsck: verify .bitmap checksums, cleanup

[PATCH 0/2] fsck: verify .bitmap checksums, cleanup

[Derrick Stolee via GitGitGadget]

Similar to the recent work on rev-indexes [1], add checks for .bitmap files
to 'git fsck'.

Patch 1 includes the full details for .bitmap files.

Patch 2 includes a cleanup of ds/fsck-pack-revindex that I noticed while
preparing this series.

Thanks, Stolee

[1]
https://lore.kernel.org/git/pull.1512.git.1681748502.gitgitgadget@gmail.com/

Derrick Stolee (2):
  fsck: verify checksums of all .bitmap files
  fsck: use local repository

 builtin/fsck.c                | 10 +++++---
 pack-bitmap.c                 | 44 +++++++++++++++++++++++++++++++++++
 pack-bitmap.h                 |  2 ++
 t/t5326-multi-pack-bitmaps.sh | 38 ++++++++++++++++++++++++++++++
 4 files changed, 91 insertions(+), 3 deletions(-)


base-commit: 48d89b51b3bb8a60580c36731b96a7206ce1e5b9
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1526%2Fderrickstolee%2Ffsck-bitmap-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1526/derrickstolee/fsck-bitmap-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/1526
-- 
gitgitgadget

[PATCH 1/2] fsck: verify checksums of all .bitmap files

[Derrick Stolee via GitGitGadget]

From: Derrick Stolee <derrickstolee@github.com>

If a filesystem-level corruption occurs in a .bitmap file, Git can react
poorly. This could take the form of a run-time error due to failing to
parse an EWAH bitmap or be more subtle such as returning the wrong set
of objects to a fetch or clone.

A natural first response to either of these kinds of errors is to run
'git fsck' to see if any files are corrupt. This currently ignores all
.bitmap files.

Add checks to 'git fsck' for all .bitmap files that are currently
associated with a multi-pack-index or pack file. Verify their checksums
using the hashfile API.

We iterate through all multi-pack-indexes and pack-files to be sure to
check all .bitmap files, not just the one that would be read by the
process. For example, a multi-pack-index bitmap overrules a pack-bitmap.
However, if the multi-pack-index is removed, the pack-bitmap may be
selected instead. Be thorough to include every file that could become
active in such a way. This includes checking files in alternates.

There is potential that we could extend this effort to check the
structure of the reachability bitmaps themselves, but it is very
expensive to do so. At minimum, it's as expensive as generating the
bitmaps in the first place, and that's assuming that we don't use the
trivial algorithm of verifying each bitmap individually. The trivial
algorithm will result in quadratic behavior (number of objects times
number of bitmapped commits) while the bitmap building operation
constructs a lattice of commits to build bitmaps incrementally and then
generate the final bitmaps from a subset of those commits.

If we were to extend 'git fsck' to check .bitmap file contents more
closely like this, then we would likely want to hide it behind an option
that signals the user is more willing to do expensive operations such as
this.

For testing, set up a repository with a pack-bitmap _and_ a
multi-pack-index bitmap. This requires some file movement to avoid
deleting the pack-bitmap during the repack that creates the
multi-pack-index bitmap. We can then verify that 'git fsck' is checking
all files, not just the "active" bitmap.

Signed-off-by: Derrick Stolee <derrickstolee@github.com>
---
 builtin/fsck.c                |  4 ++++
 pack-bitmap.c                 | 44 +++++++++++++++++++++++++++++++++++
 pack-bitmap.h                 |  2 ++
 t/t5326-multi-pack-bitmaps.sh | 38 ++++++++++++++++++++++++++++++
 4 files changed, 88 insertions(+)

diff --git a/builtin/fsck.c b/builtin/fsck.c
index 2cd461b84c1..75b30d1d00c 100644
--- a/builtin/fsck.c
+++ b/builtin/fsck.c
@@ -27,6 +27,7 @@
 #include "run-command.h"
 #include "worktree.h"
 #include "pack-revindex.h"
+#include "pack-bitmap.h"
 
 #define REACHABLE 0x0001
 #define SEEN      0x0002
@@ -57,6 +58,7 @@ static int name_objects;
 #define ERROR_COMMIT_GRAPH 020
 #define ERROR_MULTI_PACK_INDEX 040
 #define ERROR_PACK_REV_INDEX 0100
+#define ERROR_BITMAP 0200
 
 static const char *describe_object(const struct object_id *oid)
 {
@@ -1056,6 +1058,8 @@ int cmd_fsck(int argc, const char **argv, const char *prefix)
 	}
 
 	errors_found |= check_pack_rev_indexes(the_repository, show_progress);
+	if (verify_bitmap_files(the_repository))
+		errors_found |= ERROR_BITMAP;
 
 	check_connectivity();
 
diff --git a/pack-bitmap.c b/pack-bitmap.c
index e0fad723bf3..ded58929a81 100644
--- a/pack-bitmap.c
+++ b/pack-bitmap.c
@@ -2346,3 +2346,47 @@ int bitmap_is_preferred_refname(struct repository *r, const char *refname)
 
 	return 0;
 }
+
+static int verify_bitmap_file(const char *name)
+{
+	struct stat st;
+	unsigned char *data;
+	int fd = git_open(name);
+	int res = 0;
+
+	/* A non-existent file is valid. */
+	if (fstat(fd, &st)) {
+		close(fd);
+		return 0;
+	}
+
+	data = xmmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
+	close(fd);
+	if (!hashfile_checksum_valid(data, st.st_size))
+		res = error(_("bitmap file '%s' has invalid checksum"),
+			    name);
+
+	munmap(data, st.st_size);
+	return res;
+}
+
+int verify_bitmap_files(struct repository *r)
+{
+	int res = 0;
+
+	for (struct multi_pack_index *m = get_multi_pack_index(r);
+	     m; m = m->next) {
+		char *midx_bitmap_name = midx_bitmap_filename(m);
+		res |= verify_bitmap_file(midx_bitmap_name);
+		free(midx_bitmap_name);
+	}
+
+	for (struct packed_git *p = get_all_packs(r);
+	     p; p = p->next) {
+		char *pack_bitmap_name = pack_bitmap_filename(p);
+		res |= verify_bitmap_file(pack_bitmap_name);
+		free(pack_bitmap_name);
+	}
+
+	return res;
+}
diff --git a/pack-bitmap.h b/pack-bitmap.h
index f0180b5276b..84591f041bf 100644
--- a/pack-bitmap.h
+++ b/pack-bitmap.h
@@ -111,4 +111,6 @@ int bitmap_is_midx(struct bitmap_index *bitmap_git);
 const struct string_list *bitmap_preferred_tips(struct repository *r);
 int bitmap_is_preferred_refname(struct repository *r, const char *refname);
 
+int verify_bitmap_files(struct repository *r);
+
 #endif
diff --git a/t/t5326-multi-pack-bitmaps.sh b/t/t5326-multi-pack-bitmaps.sh
index 0882cbb6e4a..d7353d8d443 100755
--- a/t/t5326-multi-pack-bitmaps.sh
+++ b/t/t5326-multi-pack-bitmaps.sh
@@ -434,4 +434,42 @@ test_expect_success 'tagged commits are selected for bitmapping' '
 	)
 '
 
+corrupt_file () {
+	chmod a+w "$1" &&
+	printf "bogus" | dd of="$1" bs=1 seek="12" conv=notrunc
+}
+
+test_expect_success 'git fsck correctly identifies good and bad bitmaps' '
+	git init valid &&
+	test_when_finished rm -rf valid &&
+
+	test_commit_bulk 20 &&
+	git repack -adbf &&
+
+	# Move pack-bitmap aside so it is not deleted
+	# in next repack.
+	packbitmap=$(ls .git/objects/pack/pack-*.bitmap) &&
+	mv "$packbitmap" "$packbitmap.bak" &&
+
+	test_commit_bulk 10 &&
+	git repack -b --write-midx &&
+	midxbitmap=$(ls .git/objects/pack/multi-pack-index-*.bitmap) &&
+
+	# Copy MIDX bitmap to backup. Copy pack bitmap from backup.
+	cp "$midxbitmap" "$midxbitmap.bak" &&
+	cp "$packbitmap.bak" "$packbitmap" &&
+
+	# fsck works at first
+	git fsck &&
+
+	corrupt_file "$packbitmap" &&
+	test_must_fail git fsck 2>err &&
+	grep "bitmap file '\''$packbitmap'\'' has invalid checksum" err &&
+
+	cp "$packbitmap.bak" "$packbitmap" &&
+	corrupt_file "$midxbitmap" &&
+	test_must_fail git fsck 2>err &&
+	grep "bitmap file '\''$midxbitmap'\'' has invalid checksum" err
+'
+
 test_done
-- 
gitgitgadget

Re: [PATCH 1/2] fsck: verify checksums of all .bitmap files

[Junio C Hamano]

"Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com> writes:

> +static int verify_bitmap_file(const char *name)
> +{
> +	struct stat st;
> +	unsigned char *data;
> +	int fd = git_open(name);
> +	int res = 0;
> +
> +	/* A non-existent file is valid. */
> +	if (fstat(fd, &st)) {
> +		close(fd);
> +		return 0;
> +	}

git_open() may return a negative value to signal an error, and
fstat() would return negative to signal its own error, and feeding
the negative fd to close() would also be an error without molesting
other open file descriptors we would want to keep, and we do not
check the return value from close(), so all of the above may be
safe, but makes us feel a bit dirty.

	/* It is OK not to have the file */
	if (fd < 0 || fstat(fd, &st)) {
		if (0 <= fd)
			close(fd);
		return 0;
	}

is probably not overly too verbose and makes the result a bit more
palatable, perhaps.

> +	data = xmmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
> +	close(fd);
> +	if (!hashfile_checksum_valid(data, st.st_size))
> +		res = error(_("bitmap file '%s' has invalid checksum"),
> +			    name);
> +
> +	munmap(data, st.st_size);
> +	return res;
> +}

OK.

> +int verify_bitmap_files(struct repository *r)
> +{
> +	int res = 0;
> +
> +	for (struct multi_pack_index *m = get_multi_pack_index(r);
> +	     m; m = m->next) {
> +		char *midx_bitmap_name = midx_bitmap_filename(m);
> +		res |= verify_bitmap_file(midx_bitmap_name);
> +		free(midx_bitmap_name);
> +	}
> +
> +	for (struct packed_git *p = get_all_packs(r);
> +	     p; p = p->next) {
> +		char *pack_bitmap_name = pack_bitmap_filename(p);
> +		res |= verify_bitmap_file(pack_bitmap_name);
> +		free(pack_bitmap_name);
> +	}
> +
> +	return res;
> +}

OK.

> diff --git a/t/t5326-multi-pack-bitmaps.sh b/t/t5326-multi-pack-bitmaps.sh
> index 0882cbb6e4a..d7353d8d443 100755
> --- a/t/t5326-multi-pack-bitmaps.sh
> +++ b/t/t5326-multi-pack-bitmaps.sh
> @@ -434,4 +434,42 @@ test_expect_success 'tagged commits are selected for bitmapping' '
>  	)
>  '
>  
> +corrupt_file () {
> +	chmod a+w "$1" &&
> +	printf "bogus" | dd of="$1" bs=1 seek="12" conv=notrunc
> +}
> +
> +test_expect_success 'git fsck correctly identifies good and bad bitmaps' '
> +	git init valid &&
> +	test_when_finished rm -rf valid &&
> +
> +	test_commit_bulk 20 &&
> +	git repack -adbf &&
> +
> +	# Move pack-bitmap aside so it is not deleted
> +	# in next repack.
> +	packbitmap=$(ls .git/objects/pack/pack-*.bitmap) &&
> +	mv "$packbitmap" "$packbitmap.bak" &&
> +
> +	test_commit_bulk 10 &&
> +	git repack -b --write-midx &&
> +	midxbitmap=$(ls .git/objects/pack/multi-pack-index-*.bitmap) &&
> +
> +	# Copy MIDX bitmap to backup. Copy pack bitmap from backup.
> +	cp "$midxbitmap" "$midxbitmap.bak" &&
> +	cp "$packbitmap.bak" "$packbitmap" &&

So, at this point, we have only one pack, and we could enable the
midx bitmap and/or pack bitmap from their .bak.  We first enable
only the pack bitmap while leaving midx bitmap disabled.

> +	# fsck works at first
> +	git fsck &&

OK.

> +	corrupt_file "$packbitmap" &&
> +	test_must_fail git fsck 2>err &&
> +	grep "bitmap file '\''$packbitmap'\'' has invalid checksum" err &&

And when the only thing enabled, i.e. pack bitmap, is broken, we
notice the breakage.  OK.

> +	cp "$packbitmap.bak" "$packbitmap" &&
> +	corrupt_file "$midxbitmap" &&

Now we repair the pack bitmap and break midx bitmap.  Both are
enabled in this case.

> +	test_must_fail git fsck 2>err &&
> +	grep "bitmap file '\''$midxbitmap'\'' has invalid checksum" err

And we notice midx bitmap is corrupt.

Is it worth checking at this point if we detect breakages in both
bitmaps, if we have pack bitmap and midx bitmap, both broken?

Other than these tiny nits, looking very good.

Thanks.

[PATCH 2/2] fsck: use local repository

[Derrick Stolee via GitGitGadget]

From: Derrick Stolee <derrickstolee@github.com>

In 0d30feef3c5 (fsck: create scaffolding for rev-index checks,
2023-04-17) and later 5a6072f631d (fsck: validate .rev file header,
2023-04-17), the check_pack_rev_indexes() method was created with a
'struct repository *r' parameter. However, this parameter was unused and
instead 'the_repository' was used in its place.

Fix this situation with the obvious replacement.

Signed-off-by: Derrick Stolee <derrickstolee@github.com>
---
 builtin/fsck.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/builtin/fsck.c b/builtin/fsck.c
index 75b30d1d00c..dcc165bf0c5 100644
--- a/builtin/fsck.c
+++ b/builtin/fsck.c
@@ -869,20 +869,20 @@ static int check_pack_rev_indexes(struct repository *r, int show_progress)
 	int res = 0;
 
 	if (show_progress) {
-		for (struct packed_git *p = get_all_packs(the_repository); p; p = p->next)
+		for (struct packed_git *p = get_all_packs(r); p; p = p->next)
 			pack_count++;
 		progress = start_delayed_progress("Verifying reverse pack-indexes", pack_count);
 		pack_count = 0;
 	}
 
-	for (struct packed_git *p = get_all_packs(the_repository); p; p = p->next) {
+	for (struct packed_git *p = get_all_packs(r); p; p = p->next) {
 		int load_error = load_pack_revindex_from_disk(p);
 
 		if (load_error < 0) {
 			error(_("unable to load rev-index for pack '%s'"), p->pack_name);
 			res = ERROR_PACK_REV_INDEX;
 		} else if (!load_error &&
-			   !load_pack_revindex(the_repository, p) &&
+			   !load_pack_revindex(r, p) &&
 			   verify_pack_revindex(p)) {
 			error(_("invalid rev-index for pack '%s'"), p->pack_name);
 			res = ERROR_PACK_REV_INDEX;
-- 
gitgitgadget

Re: [PATCH 2/2] fsck: use local repository

[Junio C Hamano]

"Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com> writes:

> From: Derrick Stolee <derrickstolee@github.com>
>
> In 0d30feef3c5 (fsck: create scaffolding for rev-index checks,
> 2023-04-17) and later 5a6072f631d (fsck: validate .rev file header,
> 2023-04-17), the check_pack_rev_indexes() method was created with a
> 'struct repository *r' parameter. However, this parameter was unused and
> instead 'the_repository' was used in its place.
>
> Fix this situation with the obvious replacement.

Indeed obvious it is.  Thanks, will queue.

>
> Signed-off-by: Derrick Stolee <derrickstolee@github.com>
> ---
>  builtin/fsck.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/builtin/fsck.c b/builtin/fsck.c
> index 75b30d1d00c..dcc165bf0c5 100644
> --- a/builtin/fsck.c
> +++ b/builtin/fsck.c
> @@ -869,20 +869,20 @@ static int check_pack_rev_indexes(struct repository *r, int show_progress)
>  	int res = 0;
>  
>  	if (show_progress) {
> -		for (struct packed_git *p = get_all_packs(the_repository); p; p = p->next)
> +		for (struct packed_git *p = get_all_packs(r); p; p = p->next)
>  			pack_count++;
>  		progress = start_delayed_progress("Verifying reverse pack-indexes", pack_count);
>  		pack_count = 0;
>  	}
>  
> -	for (struct packed_git *p = get_all_packs(the_repository); p; p = p->next) {
> +	for (struct packed_git *p = get_all_packs(r); p; p = p->next) {
>  		int load_error = load_pack_revindex_from_disk(p);
>  
>  		if (load_error < 0) {
>  			error(_("unable to load rev-index for pack '%s'"), p->pack_name);
>  			res = ERROR_PACK_REV_INDEX;
>  		} else if (!load_error &&
> -			   !load_pack_revindex(the_repository, p) &&
> +			   !load_pack_revindex(r, p) &&
>  			   verify_pack_revindex(p)) {
>  			error(_("invalid rev-index for pack '%s'"), p->pack_name);
>  			res = ERROR_PACK_REV_INDEX;

[PATCH v2 0/2] fsck: verify .bitmap checksums, cleanup

[Derrick Stolee via GitGitGadget]

Similar to the recent work on rev-indexes [1], add checks for .bitmap files
to 'git fsck'.

Patch 1 includes the full details for .bitmap files.

Patch 2 includes a cleanup of ds/fsck-pack-revindex that I noticed while
preparing this series.


Updates since v2
================

 * The code for verify_bitmap_file() added checks for a negative file
   descriptor, as well as some other cleanup.
 * The test in t5326 is expanded to include the "both are corrupt" case, as
   well as a reorganization because the test was not confined to an inner
   repo.

Thanks, Stolee

[1]
https://lore.kernel.org/git/pull.1512.git.1681748502.gitgitgadget@gmail.com/

Derrick Stolee (2):
  fsck: verify checksums of all .bitmap files
  fsck: use local repository

 builtin/fsck.c                | 10 +++++---
 pack-bitmap.c                 | 45 +++++++++++++++++++++++++++++++++++
 pack-bitmap.h                 |  2 ++
 t/t5326-multi-pack-bitmaps.sh | 44 ++++++++++++++++++++++++++++++++++
 4 files changed, 98 insertions(+), 3 deletions(-)


base-commit: 48d89b51b3bb8a60580c36731b96a7206ce1e5b9
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1526%2Fderrickstolee%2Ffsck-bitmap-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1526/derrickstolee/fsck-bitmap-v2
Pull-Request: https://github.com/gitgitgadget/git/pull/1526

Range-diff vs v1:

 1:  d608d2faa86 ! 1:  5d6d6658633 fsck: verify checksums of all .bitmap files
     @@ pack-bitmap.c: int bitmap_is_preferred_refname(struct repository *r, const char
      +	int fd = git_open(name);
      +	int res = 0;
      +
     -+	/* A non-existent file is valid. */
     -+	if (fstat(fd, &st)) {
     -+		close(fd);
     ++	/* It is OK to not have the file. */
     ++	if (fd < 0 || fstat(fd, &st)) {
     ++		if (fd >= 0)
     ++			close(fd);
      +		return 0;
      +	}
      +
     @@ t/t5326-multi-pack-bitmaps.sh: test_expect_success 'tagged commits are selected
      +	cp "$packbitmap.bak" "$packbitmap" &&
      +
      +	# fsck works at first
     -+	git fsck &&
     ++	git fsck 2>err &&
     ++	test_must_be_empty err &&
      +
      +	corrupt_file "$packbitmap" &&
      +	test_must_fail git fsck 2>err &&
     @@ t/t5326-multi-pack-bitmaps.sh: test_expect_success 'tagged commits are selected
      +	cp "$packbitmap.bak" "$packbitmap" &&
      +	corrupt_file "$midxbitmap" &&
      +	test_must_fail git fsck 2>err &&
     -+	grep "bitmap file '\''$midxbitmap'\'' has invalid checksum" err
     ++	grep "bitmap file '\''$midxbitmap'\'' has invalid checksum" err &&
     ++
     ++	corrupt_file "$packbitmap" &&
     ++	test_must_fail git fsck 2>err &&
     ++	grep "bitmap file '\''$midxbitmap'\'' has invalid checksum" err &&
     ++	grep "bitmap file '\''$packbitmap'\'' has invalid checksum" err
      +'
      +
       test_done
 2:  2162a352a46 = 2:  00789bbc558 fsck: use local repository

-- 
gitgitgadget

[PATCH v2 1/2] fsck: verify checksums of all .bitmap files

[Derrick Stolee via GitGitGadget]

From: Derrick Stolee <derrickstolee@github.com>

If a filesystem-level corruption occurs in a .bitmap file, Git can react
poorly. This could take the form of a run-time error due to failing to
parse an EWAH bitmap or be more subtle such as returning the wrong set
of objects to a fetch or clone.

A natural first response to either of these kinds of errors is to run
'git fsck' to see if any files are corrupt. This currently ignores all
.bitmap files.

Add checks to 'git fsck' for all .bitmap files that are currently
associated with a multi-pack-index or pack file. Verify their checksums
using the hashfile API.

We iterate through all multi-pack-indexes and pack-files to be sure to
check all .bitmap files, not just the one that would be read by the
process. For example, a multi-pack-index bitmap overrules a pack-bitmap.
However, if the multi-pack-index is removed, the pack-bitmap may be
selected instead. Be thorough to include every file that could become
active in such a way. This includes checking files in alternates.

There is potential that we could extend this effort to check the
structure of the reachability bitmaps themselves, but it is very
expensive to do so. At minimum, it's as expensive as generating the
bitmaps in the first place, and that's assuming that we don't use the
trivial algorithm of verifying each bitmap individually. The trivial
algorithm will result in quadratic behavior (number of objects times
number of bitmapped commits) while the bitmap building operation
constructs a lattice of commits to build bitmaps incrementally and then
generate the final bitmaps from a subset of those commits.

If we were to extend 'git fsck' to check .bitmap file contents more
closely like this, then we would likely want to hide it behind an option
that signals the user is more willing to do expensive operations such as
this.

For testing, set up a repository with a pack-bitmap _and_ a
multi-pack-index bitmap. This requires some file movement to avoid
deleting the pack-bitmap during the repack that creates the
multi-pack-index bitmap. We can then verify that 'git fsck' is checking
all files, not just the "active" bitmap.

Signed-off-by: Derrick Stolee <derrickstolee@github.com>
---
 builtin/fsck.c                |  4 ++++
 pack-bitmap.c                 | 45 +++++++++++++++++++++++++++++++++++
 pack-bitmap.h                 |  2 ++
 t/t5326-multi-pack-bitmaps.sh | 44 ++++++++++++++++++++++++++++++++++
 4 files changed, 95 insertions(+)

diff --git a/builtin/fsck.c b/builtin/fsck.c
index 2cd461b84c1..75b30d1d00c 100644
--- a/builtin/fsck.c
+++ b/builtin/fsck.c
@@ -27,6 +27,7 @@
 #include "run-command.h"
 #include "worktree.h"
 #include "pack-revindex.h"
+#include "pack-bitmap.h"
 
 #define REACHABLE 0x0001
 #define SEEN      0x0002
@@ -57,6 +58,7 @@ static int name_objects;
 #define ERROR_COMMIT_GRAPH 020
 #define ERROR_MULTI_PACK_INDEX 040
 #define ERROR_PACK_REV_INDEX 0100
+#define ERROR_BITMAP 0200
 
 static const char *describe_object(const struct object_id *oid)
 {
@@ -1056,6 +1058,8 @@ int cmd_fsck(int argc, const char **argv, const char *prefix)
 	}
 
 	errors_found |= check_pack_rev_indexes(the_repository, show_progress);
+	if (verify_bitmap_files(the_repository))
+		errors_found |= ERROR_BITMAP;
 
 	check_connectivity();
 
diff --git a/pack-bitmap.c b/pack-bitmap.c
index e0fad723bf3..999f962602d 100644
--- a/pack-bitmap.c
+++ b/pack-bitmap.c
@@ -2346,3 +2346,48 @@ int bitmap_is_preferred_refname(struct repository *r, const char *refname)
 
 	return 0;
 }
+
+static int verify_bitmap_file(const char *name)
+{
+	struct stat st;
+	unsigned char *data;
+	int fd = git_open(name);
+	int res = 0;
+
+	/* It is OK to not have the file. */
+	if (fd < 0 || fstat(fd, &st)) {
+		if (fd >= 0)
+			close(fd);
+		return 0;
+	}
+
+	data = xmmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
+	close(fd);
+	if (!hashfile_checksum_valid(data, st.st_size))
+		res = error(_("bitmap file '%s' has invalid checksum"),
+			    name);
+
+	munmap(data, st.st_size);
+	return res;
+}
+
+int verify_bitmap_files(struct repository *r)
+{
+	int res = 0;
+
+	for (struct multi_pack_index *m = get_multi_pack_index(r);
+	     m; m = m->next) {
+		char *midx_bitmap_name = midx_bitmap_filename(m);
+		res |= verify_bitmap_file(midx_bitmap_name);
+		free(midx_bitmap_name);
+	}
+
+	for (struct packed_git *p = get_all_packs(r);
+	     p; p = p->next) {
+		char *pack_bitmap_name = pack_bitmap_filename(p);
+		res |= verify_bitmap_file(pack_bitmap_name);
+		free(pack_bitmap_name);
+	}
+
+	return res;
+}
diff --git a/pack-bitmap.h b/pack-bitmap.h
index f0180b5276b..84591f041bf 100644
--- a/pack-bitmap.h
+++ b/pack-bitmap.h
@@ -111,4 +111,6 @@ int bitmap_is_midx(struct bitmap_index *bitmap_git);
 const struct string_list *bitmap_preferred_tips(struct repository *r);
 int bitmap_is_preferred_refname(struct repository *r, const char *refname);
 
+int verify_bitmap_files(struct repository *r);
+
 #endif
diff --git a/t/t5326-multi-pack-bitmaps.sh b/t/t5326-multi-pack-bitmaps.sh
index 0882cbb6e4a..f771c442d41 100755
--- a/t/t5326-multi-pack-bitmaps.sh
+++ b/t/t5326-multi-pack-bitmaps.sh
@@ -434,4 +434,48 @@ test_expect_success 'tagged commits are selected for bitmapping' '
 	)
 '
 
+corrupt_file () {
+	chmod a+w "$1" &&
+	printf "bogus" | dd of="$1" bs=1 seek="12" conv=notrunc
+}
+
+test_expect_success 'git fsck correctly identifies good and bad bitmaps' '
+	git init valid &&
+	test_when_finished rm -rf valid &&
+
+	test_commit_bulk 20 &&
+	git repack -adbf &&
+
+	# Move pack-bitmap aside so it is not deleted
+	# in next repack.
+	packbitmap=$(ls .git/objects/pack/pack-*.bitmap) &&
+	mv "$packbitmap" "$packbitmap.bak" &&
+
+	test_commit_bulk 10 &&
+	git repack -b --write-midx &&
+	midxbitmap=$(ls .git/objects/pack/multi-pack-index-*.bitmap) &&
+
+	# Copy MIDX bitmap to backup. Copy pack bitmap from backup.
+	cp "$midxbitmap" "$midxbitmap.bak" &&
+	cp "$packbitmap.bak" "$packbitmap" &&
+
+	# fsck works at first
+	git fsck 2>err &&
+	test_must_be_empty err &&
+
+	corrupt_file "$packbitmap" &&
+	test_must_fail git fsck 2>err &&
+	grep "bitmap file '\''$packbitmap'\'' has invalid checksum" err &&
+
+	cp "$packbitmap.bak" "$packbitmap" &&
+	corrupt_file "$midxbitmap" &&
+	test_must_fail git fsck 2>err &&
+	grep "bitmap file '\''$midxbitmap'\'' has invalid checksum" err &&
+
+	corrupt_file "$packbitmap" &&
+	test_must_fail git fsck 2>err &&
+	grep "bitmap file '\''$midxbitmap'\'' has invalid checksum" err &&
+	grep "bitmap file '\''$packbitmap'\'' has invalid checksum" err
+'
+
 test_done
-- 
gitgitgadget

[PATCH v2 2/2] fsck: use local repository

[Derrick Stolee via GitGitGadget]

From: Derrick Stolee <derrickstolee@github.com>

In 0d30feef3c5 (fsck: create scaffolding for rev-index checks,
2023-04-17) and later 5a6072f631d (fsck: validate .rev file header,
2023-04-17), the check_pack_rev_indexes() method was created with a
'struct repository *r' parameter. However, this parameter was unused and
instead 'the_repository' was used in its place.

Fix this situation with the obvious replacement.

Signed-off-by: Derrick Stolee <derrickstolee@github.com>
---
 builtin/fsck.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/builtin/fsck.c b/builtin/fsck.c
index 75b30d1d00c..dcc165bf0c5 100644
--- a/builtin/fsck.c
+++ b/builtin/fsck.c
@@ -869,20 +869,20 @@ static int check_pack_rev_indexes(struct repository *r, int show_progress)
 	int res = 0;
 
 	if (show_progress) {
-		for (struct packed_git *p = get_all_packs(the_repository); p; p = p->next)
+		for (struct packed_git *p = get_all_packs(r); p; p = p->next)
 			pack_count++;
 		progress = start_delayed_progress("Verifying reverse pack-indexes", pack_count);
 		pack_count = 0;
 	}
 
-	for (struct packed_git *p = get_all_packs(the_repository); p; p = p->next) {
+	for (struct packed_git *p = get_all_packs(r); p; p = p->next) {
 		int load_error = load_pack_revindex_from_disk(p);
 
 		if (load_error < 0) {
 			error(_("unable to load rev-index for pack '%s'"), p->pack_name);
 			res = ERROR_PACK_REV_INDEX;
 		} else if (!load_error &&
-			   !load_pack_revindex(the_repository, p) &&
+			   !load_pack_revindex(r, p) &&
 			   verify_pack_revindex(p)) {
 			error(_("invalid rev-index for pack '%s'"), p->pack_name);
 			res = ERROR_PACK_REV_INDEX;
-- 
gitgitgadget