alpm_handle: store lock file descriptor

There was a brief window between opening the file descriptor and
creating a stream to it.  If the process was interrupted during that
window the lock file would not be removed correctly.

The pid is no longer printed to the lock file as this was virtually
meaningless for lock files on NFS.

Fixes FS#35603

Signed-off-by: Andrew Gregory <andrew.gregory.8@gmail.com>
Signed-off-by: Allan McRae <allan@archlinux.org>

2 files changed, 10 insertions, 17 deletions

diff --git a/lib/libalpm/handle.c b/lib/libalpm/handle.c
index ea033b20..1d661a2d 100644
--- a/lib/libalpm/handle.c
+++ b/lib/libalpm/handle.c
@@ -44,6 +44,7 @@ alpm_handle_t *_alpm_handle_new(void)
 
 	CALLOC(handle, 1, sizeof(alpm_handle_t), return NULL);
 	handle->deltaratio = 0.0;
+	handle->lockfd = -1;
 
 	return handle;
 }
@@ -91,11 +92,10 @@ void _alpm_handle_free(alpm_handle_t *handle)
 /** Lock the database */
 int _alpm_handle_lock(alpm_handle_t *handle)
 {
-	int fd;
 	char *dir, *ptr;
 
 	ASSERT(handle->lockfile != NULL, return -1);
-	ASSERT(handle->lckstream == NULL, return 0);
+	ASSERT(handle->lockfd < 0, return 0);
 
 	/* create the dir of the lockfile first */
 	dir = strdup(handle->lockfile);
@@ -110,27 +110,20 @@ int _alpm_handle_lock(alpm_handle_t *handle)
 	FREE(dir);
 
 	do {
-		fd = open(handle->lockfile, O_WRONLY | O_CREAT | O_EXCL, 0000);
-	} while(fd == -1 && errno == EINTR);
-	if(fd >= 0) {
-		FILE *f = fdopen(fd, "w");
-		fprintf(f, "%ld\n", (long)getpid());
-		fflush(f);
-		fsync(fd);
-		handle->lckstream = f;
-		return 0;
-	}
-	return -1;
+		handle->lockfd = open(handle->lockfile, O_WRONLY | O_CREAT | O_EXCL, 0000);
+	} while(handle->lockfd == -1 && errno == EINTR);
+
+	return (handle->lockfd >= 0 ? 0 : -1);
 }
 
 /** Remove a lock file */
 int _alpm_handle_unlock(alpm_handle_t *handle)
 {
 	ASSERT(handle->lockfile != NULL, return -1);
-	ASSERT(handle->lckstream != NULL, return 0);
+	ASSERT(handle->lockfd >= 0, return 0);
 
-	fclose(handle->lckstream);
-	handle->lckstream = NULL;
+	close(handle->lockfd);
+	handle->lockfd = -1;
 
 	if(unlink(handle->lockfile) && errno != ENOENT) {
 		return -1;
diff --git a/lib/libalpm/handle.h b/lib/libalpm/handle.h
index 5e84d586..a4e2cf72 100644
--- a/lib/libalpm/handle.h
+++ b/lib/libalpm/handle.h
@@ -55,7 +55,7 @@ struct __alpm_handle_t {
 	alpm_db_t *db_local;       /* local db pointer */
 	alpm_list_t *dbs_sync;  /* List of (alpm_db_t *) */
 	FILE *logstream;        /* log file stream pointer */
-	FILE *lckstream;        /* lock file stream pointer if one exists */
+	int lockfd;             /* lock file descriptor */
 	alpm_trans_t *trans;
 
 #ifdef HAVE_LIBCURL