* [PATCH 4/5] merge-ort: abort merge when trees have duplicate entries
2026-04-21 0:26 [PATCH 0/5] Duplicate entry hardening Elijah Newren via GitGitGadget
` (2 preceding siblings ...)
2026-04-21 0:26 ` [PATCH 3/5] merge-ort: free diff pairs queue in clear_or_reinit_internal_opts() Elijah Newren via GitGitGadget
@ 2026-04-21 0:26 ` Elijah Newren via GitGitGadget
2026-04-21 0:26 ` [PATCH 5/5] cache-tree: fix verify_cache() to catch non-adjacent D/F conflicts Elijah Newren via GitGitGadget
4 siblings, 0 replies; 6+ messages in thread
From: Elijah Newren via GitGitGadget @ 2026-04-21 0:26 UTC (permalink / raw)
To: git; +Cc: Elijah Newren, Elijah Newren
From: Elijah Newren <newren@gmail.com>
Trees with duplicate entries are malformed; fsck reports "contains
duplicate file entries" for them. merge-ort has from the beginning
assumed that we would never hit such trees. It was written with the
assumption that traverse_trees() calls collect_merge_info_callback() at
most once per path. The "sanity checks" in that callback (added in
d2bc1994f363 (merge-ort: implement a very basic collect_merge_info(),
2020-12-13)) verify properties of each individual call but not that
invariant. The strmap_put() in setup_path_info() silently overwrites
the entry from any prior call for the same path, because it assumed
there would be no other path. Unfortunately, supplemental data
structures for various optimizations could still be tweaked before the
extra paths were overwritten, and those data structures not matching
expected state could trip various assertions.
Change the return type of setup_path_info() from void to int to allow us
to detect this case, and abort the merge with a clear error message when
it occurs.
Signed-off-by: Elijah Newren <newren@gmail.com>
---
merge-ort.c | 61 ++++++++++++++++------------
t/t6422-merge-rename-corner-cases.sh | 54 ++++++++++++++++++++++++
2 files changed, 88 insertions(+), 27 deletions(-)
diff --git a/merge-ort.c b/merge-ort.c
index 8f911cb639..be0829bbb7 100644
--- a/merge-ort.c
+++ b/merge-ort.c
@@ -1026,18 +1026,18 @@ static int traverse_trees_wrapper(struct index_state *istate,
return ret < 0 ? ret : 0;
}
-static void setup_path_info(struct merge_options *opt,
- struct string_list_item *result,
- const char *current_dir_name,
- int current_dir_name_len,
- char *fullpath, /* we'll take over ownership */
- struct name_entry *names,
- struct name_entry *merged_version,
- unsigned is_null, /* boolean */
- unsigned df_conflict, /* boolean */
- unsigned filemask,
- unsigned dirmask,
- int resolved /* boolean */)
+static int setup_path_info(struct merge_options *opt,
+ struct string_list_item *result,
+ const char *current_dir_name,
+ int current_dir_name_len,
+ char *fullpath, /* we'll take over ownership */
+ struct name_entry *names,
+ struct name_entry *merged_version,
+ unsigned is_null, /* boolean */
+ unsigned df_conflict, /* boolean */
+ unsigned filemask,
+ unsigned dirmask,
+ int resolved /* boolean */)
{
/* result->util is void*, so mi is a convenience typed variable */
struct merged_info *mi;
@@ -1081,9 +1081,11 @@ static void setup_path_info(struct merge_options *opt,
*/
mi->is_null = 1;
}
- strmap_put(&opt->priv->paths, fullpath, mi);
+ if (strmap_put(&opt->priv->paths, fullpath, mi))
+ return error(_("tree has duplicate entries for '%s'"), fullpath);
result->string = fullpath;
result->util = mi;
+ return 0;
}
static void add_pair(struct merge_options *opt,
@@ -1350,9 +1352,10 @@ static int collect_merge_info_callback(int n,
*/
if (side1_matches_mbase && side2_matches_mbase) {
/* mbase, side1, & side2 all match; use mbase as resolution */
- setup_path_info(opt, &pi, dirname, info->pathlen, fullpath,
- names, names+0, mbase_null, 0 /* df_conflict */,
- filemask, dirmask, 1 /* resolved */);
+ if (setup_path_info(opt, &pi, dirname, info->pathlen, fullpath,
+ names, names+0, mbase_null, 0 /* df_conflict */,
+ filemask, dirmask, 1 /* resolved */))
+ return -1; /* Quit traversing */
return mask;
}
@@ -1364,9 +1367,10 @@ static int collect_merge_info_callback(int n,
*/
if (sides_match && filemask == 0x07) {
/* use side1 (== side2) version as resolution */
- setup_path_info(opt, &pi, dirname, info->pathlen, fullpath,
- names, names+1, side1_null, 0,
- filemask, dirmask, 1);
+ if (setup_path_info(opt, &pi, dirname, info->pathlen, fullpath,
+ names, names+1, side1_null, 0,
+ filemask, dirmask, 1))
+ return -1; /* Quit traversing */
return mask;
}
@@ -1378,18 +1382,20 @@ static int collect_merge_info_callback(int n,
*/
if (side1_matches_mbase && filemask == 0x07) {
/* use side2 version as resolution */
- setup_path_info(opt, &pi, dirname, info->pathlen, fullpath,
- names, names+2, side2_null, 0,
- filemask, dirmask, 1);
+ if (setup_path_info(opt, &pi, dirname, info->pathlen, fullpath,
+ names, names+2, side2_null, 0,
+ filemask, dirmask, 1))
+ return -1; /* Quit traversing */
return mask;
}
/* Similar to above but swapping sides 1 and 2 */
if (side2_matches_mbase && filemask == 0x07) {
/* use side1 version as resolution */
- setup_path_info(opt, &pi, dirname, info->pathlen, fullpath,
- names, names+1, side1_null, 0,
- filemask, dirmask, 1);
+ if (setup_path_info(opt, &pi, dirname, info->pathlen, fullpath,
+ names, names+1, side1_null, 0,
+ filemask, dirmask, 1))
+ return -1; /* Quit traversing */
return mask;
}
@@ -1413,8 +1419,9 @@ static int collect_merge_info_callback(int n,
* unconflict some more cases, but that comes later so all we can
* do now is record the different non-null file hashes.)
*/
- setup_path_info(opt, &pi, dirname, info->pathlen, fullpath,
- names, NULL, 0, df_conflict, filemask, dirmask, 0);
+ if (setup_path_info(opt, &pi, dirname, info->pathlen, fullpath,
+ names, NULL, 0, df_conflict, filemask, dirmask, 0))
+ return -1; /* Quit traversing */
ci = pi.util;
VERIFY_CI(ci);
diff --git a/t/t6422-merge-rename-corner-cases.sh b/t/t6422-merge-rename-corner-cases.sh
index e18d5a227d..81b645bb3b 100755
--- a/t/t6422-merge-rename-corner-cases.sh
+++ b/t/t6422-merge-rename-corner-cases.sh
@@ -1525,4 +1525,58 @@ test_expect_success 'submodule/directory preliminary conflict' '
)
'
+# Testcase: submodule/directory conflict with duplicate tree entries
+# One side has a path as a gitlink (submodule). The other side replaces
+# the gitlink with a directory. A third-party tool creates a tree on the
+# submodule side that has *both* a gitlink and a tree entry for the same
+# path (adding a file inside the submodule path ignoring that there's a
+# gitlink there). collect_merge_info_callback() should detect the
+# duplicate and abort rather than silently corrupting its bookkeeping.
+
+test_expect_success 'duplicate tree entries trigger an error' '
+ test_when_finished "rm -rf duplicate-entry" &&
+ git init duplicate-entry &&
+ (
+ cd duplicate-entry &&
+
+ # Base commit: "docs" is a gitlink (submodule)
+ empty_tree=$(git mktree </dev/null) &&
+ fake_commit=$(git commit-tree $empty_tree </dev/null) &&
+ git update-index --add --cacheinfo 160000,$fake_commit,docs &&
+ echo base >file.txt &&
+ git add file.txt &&
+ git commit -m base &&
+
+ # side1: remove the gitlink, replace with a directory
+ git checkout -b side1 &&
+ git rm --cached docs &&
+ mkdir -p docs &&
+ echo hello >docs/requirements.txt &&
+ git add docs/requirements.txt &&
+ git commit -m "side1: submodule to directory" &&
+
+ # side2: keep the gitlink but craft a tree that also
+ # contains a tree entry for "docs" (simulating a tool
+ # that adds files inside a submodule path without
+ # removing the gitlink first).
+ git checkout main &&
+ git checkout -b side2 &&
+ blob_oid=$(echo world | git hash-object -w --stdin) &&
+ docs_tree=$(printf "100644 blob %s\trequirements.txt\n" \
+ "$blob_oid" | git mktree) &&
+ cur_tree=$(git rev-parse HEAD^{tree}) &&
+ git cat-file -p $cur_tree >tree-listing &&
+ printf "040000 tree %s\tdocs\n" "$docs_tree" >>tree-listing &&
+ new_tree=$(git mktree <tree-listing) &&
+ side2_commit=$(git commit-tree $new_tree -p HEAD \
+ -m "side2: add file alongside submodule") &&
+ git update-ref refs/heads/side2 $side2_commit &&
+
+ # Merging must detect the duplicate and abort
+ git checkout side1 &&
+ test_must_fail git merge side2 2>err &&
+ test_grep "duplicate entries" err
+ )
+'
+
test_done
--
gitgitgadget
^ permalink raw reply related [flat|nested] 6+ messages in thread* [PATCH 5/5] cache-tree: fix verify_cache() to catch non-adjacent D/F conflicts
2026-04-21 0:26 [PATCH 0/5] Duplicate entry hardening Elijah Newren via GitGitGadget
` (3 preceding siblings ...)
2026-04-21 0:26 ` [PATCH 4/5] merge-ort: abort merge when trees have duplicate entries Elijah Newren via GitGitGadget
@ 2026-04-21 0:26 ` Elijah Newren via GitGitGadget
4 siblings, 0 replies; 6+ messages in thread
From: Elijah Newren via GitGitGadget @ 2026-04-21 0:26 UTC (permalink / raw)
To: git; +Cc: Elijah Newren, Elijah Newren
From: Elijah Newren <newren@gmail.com>
verify_cache() checks that the index does not contain both "path" and
"path/file" before writing a tree. It does this by comparing only
adjacent entries, relying on the assumption that "path/file" would
immediately follow "path" in sorted order. Unfortunately, this
assumption does not always hold. For example:
docs <-- submodule entry
docs-internal/README.md <-- intervening entry
docs/requirements.txt <-- D/F conflict, NOT adjacent to "docs"
When this happens, verify_cache() silently misses the D/F conflict and
write-tree produces a corrupt tree object containing duplicate entries
(one for the submodule "docs" and one for the tree "docs").
I could not find any caller in current git that both allows the index to
get into this state and then tries to write it out without doing other
checks beyond the verify_cache() call in cache_tree_update(), but
verify_cache() is documented as a safety net for preventing corrupt
trees and should actually provide that guarantee. A downstream consumer
that relied solely on cache_tree_update()'s internal checking via
verify_cache() to prevent duplicate tree entries was bitten by the gap.
Add a test that constructs a corrupt index directly (bypassing the D/F
checks in add_index_entry) and verifies that write-tree now rejects it.
Signed-off-by: Elijah Newren <newren@gmail.com>
---
cache-tree.c | 46 ++++++++++++++++++++++++--
t/meson.build | 1 +
t/t0093-direct-index-write.pl | 38 ++++++++++++++++++++++
t/t0093-verify-cache-df-gap.sh | 59 ++++++++++++++++++++++++++++++++++
4 files changed, 141 insertions(+), 3 deletions(-)
create mode 100644 t/t0093-direct-index-write.pl
create mode 100755 t/t0093-verify-cache-df-gap.sh
diff --git a/cache-tree.c b/cache-tree.c
index 7881b42aa2..f11844fe72 100644
--- a/cache-tree.c
+++ b/cache-tree.c
@@ -192,22 +192,62 @@ static int verify_cache(struct index_state *istate, int flags)
for (i = 0; i + 1 < istate->cache_nr; i++) {
/* path/file always comes after path because of the way
* the cache is sorted. Also path can appear only once,
- * which means conflicting one would immediately follow.
+ * so path/file is likely the immediately following path
+ * but might be separated if there is e.g. a
+ * path-internal/... file.
*/
const struct cache_entry *this_ce = istate->cache[i];
const struct cache_entry *next_ce = istate->cache[i + 1];
const char *this_name = this_ce->name;
const char *next_name = next_ce->name;
int this_len = ce_namelen(this_ce);
+ const char *conflict_name = NULL;
+
if (this_len < ce_namelen(next_ce) &&
- next_name[this_len] == '/' &&
+ next_name[this_len] <= '/' &&
strncmp(this_name, next_name, this_len) == 0) {
+ if (next_name[this_len] == '/') {
+ conflict_name = next_name;
+ } else if (next_name[this_len] < '/') {
+ /*
+ * The immediately next entry shares our
+ * prefix but sorts before "path/" (e.g.,
+ * "path-internal" between "path" and
+ * "path/file", since '-' (0x2D) < '/'
+ * (0x2F)). Binary search to find where
+ * "path/" would be and check for a D/F
+ * conflict there.
+ */
+ struct cache_entry *other;
+ struct strbuf probe = STRBUF_INIT;
+ int pos;
+
+ strbuf_add(&probe, this_name, this_len);
+ strbuf_addch(&probe, '/');
+ pos = index_name_pos_sparse(istate,
+ probe.buf,
+ probe.len);
+ strbuf_release(&probe);
+
+ if (pos < 0)
+ pos = -pos - 1;
+ if (pos >= (int)istate->cache_nr)
+ continue;
+ other = istate->cache[pos];
+ if (ce_namelen(other) > this_len &&
+ other->name[this_len] == '/' &&
+ !strncmp(this_name, other->name, this_len))
+ conflict_name = other->name;
+ }
+ }
+
+ if (conflict_name) {
if (10 < ++funny) {
fprintf(stderr, "...\n");
break;
}
fprintf(stderr, "You have both %s and %s\n",
- this_name, next_name);
+ this_name, conflict_name);
}
}
if (funny)
diff --git a/t/meson.build b/t/meson.build
index 7528e5cda5..362177999b 100644
--- a/t/meson.build
+++ b/t/meson.build
@@ -124,6 +124,7 @@ integration_tests = [
't0090-cache-tree.sh',
't0091-bugreport.sh',
't0092-diagnose.sh',
+ 't0093-verify-cache-df-gap.sh',
't0095-bloom.sh',
't0100-previous.sh',
't0101-at-syntax.sh',
diff --git a/t/t0093-direct-index-write.pl b/t/t0093-direct-index-write.pl
new file mode 100644
index 0000000000..2881a3ebb2
--- /dev/null
+++ b/t/t0093-direct-index-write.pl
@@ -0,0 +1,38 @@
+#!/usr/bin/perl
+#
+# Build a v2 index file from entries listed on stdin.
+# Each line: "octalmode hex-oid name"
+# Output: binary index written to stdout.
+#
+# This bypasses all D/F safety checks in add_index_entry(), simulating
+# what happens when code uses ADD_CACHE_JUST_APPEND to bulk-load entries.
+use strict;
+use warnings;
+use Digest::SHA qw(sha1 sha256);
+
+my $hash_algo = $ENV{'GIT_DEFAULT_HASH'} || 'sha1';
+my $hash_func = $hash_algo eq 'sha256' ? \&sha256 : \&sha1;
+
+my @entries;
+while (my $line = <STDIN>) {
+ chomp $line;
+ my ($mode, $oid_hex, $name) = split(/ /, $line, 3);
+ push @entries, [$mode, $oid_hex, $name];
+}
+
+my $body = "DIRC" . pack("NN", 2, scalar @entries);
+
+for my $ent (@entries) {
+ my ($mode, $oid_hex, $name) = @{$ent};
+ # 10 x 32-bit stat fields (zeroed), with mode in position 7
+ my $stat = pack("N10", 0, 0, 0, 0, 0, 0, oct($mode), 0, 0, 0);
+ my $oid = pack("H*", $oid_hex);
+ my $flags = pack("n", length($name) & 0xFFF);
+ my $entry = $stat . $oid . $flags . $name . "\0";
+ # Pad to 8-byte boundary
+ while (length($entry) % 8) { $entry .= "\0"; }
+ $body .= $entry;
+}
+
+binmode STDOUT;
+print $body . $hash_func->($body);
diff --git a/t/t0093-verify-cache-df-gap.sh b/t/t0093-verify-cache-df-gap.sh
new file mode 100755
index 0000000000..0b6829d805
--- /dev/null
+++ b/t/t0093-verify-cache-df-gap.sh
@@ -0,0 +1,59 @@
+#!/bin/sh
+
+test_description='verify_cache() must catch non-adjacent D/F conflicts
+
+Ensure that verify_cache() can complain about bad entries like:
+
+ docs <-- submodule
+ docs-internal/... <-- sorts here because "-" < "/"
+ docs/... <-- D/F conflict with "docs" above, not adjacent
+
+In order to test verify_cache, we directly construct a corrupt index
+(bypassing the D/F safety checks in add_index_entry) and verify that
+write-tree rejects it.
+'
+
+. ./test-lib.sh
+
+if ! test_have_prereq PERL
+then
+ skip_all='skipping verify_cache D/F tests; Perl not available'
+ test_done
+fi
+
+# Build a v2 index from entries on stdin, bypassing D/F checks.
+# Each line: "octalmode hex-oid name" (entries must be pre-sorted).
+build_corrupt_index () {
+ perl "$TEST_DIRECTORY/t0093-direct-index-write.pl" >"$1"
+}
+
+test_expect_success 'setup objects' '
+ test_commit base &&
+ BLOB=$(git rev-parse HEAD:base.t) &&
+ SUB_COMMIT=$(git rev-parse HEAD)
+'
+
+test_expect_success 'adjacent D/F conflict is caught by verify_cache' '
+ cat >index-entries <<-EOF &&
+ 0160000 $SUB_COMMIT docs
+ 0100644 $BLOB docs/requirements.txt
+ EOF
+ build_corrupt_index .git/index <index-entries &&
+
+ test_must_fail git write-tree 2>err &&
+ test_grep "You have both docs and docs/requirements.txt" err
+'
+
+test_expect_success 'non-adjacent D/F conflict is caught by verify_cache' '
+ cat >index-entries <<-EOF &&
+ 0160000 $SUB_COMMIT docs
+ 0100644 $BLOB docs-internal/README.md
+ 0100644 $BLOB docs/requirements.txt
+ EOF
+ build_corrupt_index .git/index <index-entries &&
+
+ test_must_fail git write-tree 2>err &&
+ test_grep "You have both docs and docs/requirements.txt" err
+'
+
+test_done
--
gitgitgadget
^ permalink raw reply related [flat|nested] 6+ messages in thread