Subject: [PATCH v2] fsmonitor: fix khash memory leak in do_handle_client

From: "Paul Tarjan via GitGitGadget" <[email-masked]>
Date: Wed, 31 Dec 2025 14:39:03 +0000

From: Paul Tarjan <[email-masked]>

The do_handle_client() function allocates a khash table to de-duplicate
pathnames when responding to client requests. However, kh_release_str()
was used instead of kh_destroy_str(). The release function only frees
internal arrays (flags, keys, vals) but not the struct itself, which is
allocated by kh_init_str() via xcalloc. This caused a 40-byte leak per
client request.

Fix by using kh_destroy_str() which properly frees both internal arrays
and the struct itself. Also move the cleanup to the cleanup section and
initialize shown to NULL so that kh_destroy_str() is safe to call on all
exit paths.

Signed-off-by: Paul Tarjan <[email-masked]>
---
    fsmonitor: fix khash memory leak in do_handle_client
    
    The do_handle_client() function allocates a khash table to de-duplicate
    pathnames when responding to client requests. However, kh_release_str()
    was used instead of kh_destroy_str(). The release function only frees
    internal arrays (flags, keys, vals) but not the struct itself, which is
    allocated by kh_init_str() via xcalloc. This caused a 40-byte leak per
    client request.
    
    Fix by using kh_destroy_str() which properly frees both internal arrays
    and the struct itself. Also move the cleanup to the cleanup section and
    initialize shown to NULL so that kh_destroy_str() is safe to call on all
    exit paths.
    
    Changes since v1:
    
     * Removed incorrect claim about interrupted threads reaching cleanup
     * Simplified commit message to focus on the real bug (kh_release vs
       kh_destroy)
    
    Signed-off-by: Paul Tarjan [email-masked]

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-2148%2Fptarjan%2Fclaude%2Ffix-fsmonitor-hashmap-leak-gfDCU-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-2148/ptarjan/claude/fix-fsmonitor-hashmap-leak-gfDCU-v2
Pull-Request: https://github.com/git/git/pull/2148

Range-diff vs v1:

 1:  18670d3230 ! 1:  0a754c7f09 fsmonitor: fix khash memory leak in do_handle_client
     @@ Commit message
          fsmonitor: fix khash memory leak in do_handle_client
      
          The do_handle_client() function allocates a khash table to de-duplicate
     -    pathnames when responding to client requests. Two issues existed:
     +    pathnames when responding to client requests. However, kh_release_str()
     +    was used instead of kh_destroy_str(). The release function only frees
     +    internal arrays (flags, keys, vals) but not the struct itself, which is
     +    allocated by kh_init_str() via xcalloc. This caused a 40-byte leak per
     +    client request.
      
     -    1. kh_release_str() was used instead of kh_destroy_str(). The release
     -       function only frees internal arrays (flags, keys, vals) but not the
     -       struct itself (allocated by kh_init_str via xcalloc). This caused a
     -       40-byte leak per request.
     +    Fix by using kh_destroy_str() which properly frees both internal arrays
     +    and the struct itself. Also move the cleanup to the cleanup section and
     +    initialize shown to NULL so that kh_destroy_str() is safe to call on all
     +    exit paths.
      
     -    2. The khash was freed mid-function rather than in the cleanup section,
     -       so if the worker thread was interrupted before reaching that point
     -       during daemon shutdown, the memory would leak.
     -
     -    Fix both issues by:
     -    - Initializing shown = NULL at declaration
     -    - Using kh_destroy_str() which handles NULL and frees both internal
     -      arrays and the struct itself
     -    - Moving the cleanup to the cleanup section so it runs on all exit paths
     -
     -    Signed-off-by: Claude <[email-masked]>
     +    Signed-off-by: Paul Tarjan <[email-masked]>
      
       ## builtin/fsmonitor--daemon.c ##
      @@ builtin/fsmonitor--daemon.c: static int do_handle_client(struct fsmonitor_daemon_state *state,

 builtin/fsmonitor--daemon.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/builtin/fsmonitor--daemon.c b/builtin/fsmonitor--daemon.c
index 242c594646..bc4571938c 100644
--- a/builtin/fsmonitor--daemon.c
+++ b/builtin/fsmonitor--daemon.c
@@ -671,7 +671,7 @@ static int do_handle_client(struct fsmonitor_daemon_state *state,
 	const struct fsmonitor_batch *batch;
 	struct fsmonitor_batch *remainder = NULL;
 	intmax_t count = 0, duplicates = 0;
-	kh_str_t *shown;
+	kh_str_t *shown = NULL;
 	int hash_ret;
 	int do_trivial = 0;
 	int do_flush = 0;
@@ -909,8 +909,6 @@ static int do_handle_client(struct fsmonitor_daemon_state *state,
 		total_response_len += payload.len;
 	}
 
-	kh_release_str(shown);
-
 	pthread_mutex_lock(&state->main_lock);
 
 	if (token_data->client_ref_count > 0)
@@ -954,6 +952,7 @@ static int do_handle_client(struct fsmonitor_daemon_state *state,
 	trace2_data_intmax("fsmonitor", the_repository, "response/count/duplicates", duplicates);
 
 cleanup:
+	kh_destroy_str(shown);
 	strbuf_release(&response_token);
 	strbuf_release(&requested_token_id);
 	strbuf_release(&payload);

base-commit: 7c7698a654a7a0031f65b0ab0c1c4e438e95df60
-- 
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