From a60bbf1a4590ae7ca359e1456f67e7a992698fd7 Mon Sep 17 00:00:00 2001
From: Allan McRae <allan@archlinux.org>
Date: Thu, 8 May 2025 23:00:57 +1000
Subject: [PATCH] Do not chown downloads when DownloadUser is unset

On NFS caches, using chown to change file permissions to the UID 0 user
will fail due to root_squash.  When DownloadUser is unset, or set to
the UID 0 user (root), avoid the unneeded chown calls providing a
workaround.

Fixes #194

Signed-off-by: Allan McRae <allan@archlinux.org>
---
 lib/libalpm/dload.c | 24 ++++++++++++++----------
 1 file changed, 14 insertions(+), 10 deletions(-)

diff --git a/lib/libalpm/dload.c b/lib/libalpm/dload.c
index 6db187d7..c5de0e6e 100644
--- a/lib/libalpm/dload.c
+++ b/lib/libalpm/dload.c
@@ -73,17 +73,21 @@ static mode_t _getumask(void)
 	return mask;
 }
 
-static int finalize_download_file(const char *filename)
+static int finalize_download_file(const char *filename, const char *user)
 {
 	struct stat st;
 	uid_t myuid = getuid();
+	struct passwd const *pw = NULL;
+
 	ASSERT(filename != NULL, return -1);
 	ASSERT(stat(filename, &st) == 0, return -1);
+	ASSERT((pw = getpwuid(0)) != NULL, return -1);
+
 	if(st.st_size == 0) {
 		unlink(filename);
                 return 1;
 	}
-	if(myuid == 0) {
+	if(myuid == 0 && strcmp(user, pw->pw_name) != 0) {
 		ASSERT(chown(filename, 0, 0) != -1, return -1);
 	}
 	ASSERT(chmod(filename, ~(_getumask()) & 0666) != -1, return -1);
@@ -1080,11 +1084,11 @@ static int payload_download_fetchcb(struct dload_payload *payload,
 	return ret;
 }
 
-static int move_file(const char *filepath, const char *directory)
+static int move_file(const char *filepath, const char *directory, const char *user)
 {
 	ASSERT(filepath != NULL, return -1);
 	ASSERT(directory != NULL, return -1);
-	int ret = finalize_download_file(filepath);
+	int ret = finalize_download_file(filepath, user);
 	if(ret != 0) {
 		return ret;
 	}
@@ -1098,7 +1102,7 @@ static int move_file(const char *filepath, const char *directory)
 	return 0;
 }
 
-static int finalize_download_locations(alpm_list_t *payloads, const char *localpath)
+static int finalize_download_locations(alpm_list_t *payloads, const char *localpath, const char *user)
 {
 	ASSERT(payloads != NULL, return -1);
 	ASSERT(localpath != NULL, return -1);
@@ -1107,10 +1111,10 @@ static int finalize_download_locations(alpm_list_t *payloads, const char *localp
 	for(p = payloads; p; p = p->next) {
 		struct dload_payload *payload = p->data;
 		if(payload->tempfile_name) {
-			move_file(payload->tempfile_name, localpath);
+			move_file(payload->tempfile_name, localpath, user);
 		}
 		if(payload->destfile_name) {
-			int ret = move_file(payload->destfile_name, localpath);
+			int ret = move_file(payload->destfile_name, localpath, user);
 
 			if(ret == -1) {
 				/* ignore error if the file already existed - only signature file was downloaded */
@@ -1127,7 +1131,7 @@ static int finalize_download_locations(alpm_list_t *payloads, const char *localp
 				size_t sig_filename_len = strlen(payload->destfile_name) + sizeof(sig_suffix);
 				MALLOC(sig_filename, sig_filename_len, continue);
 				snprintf(sig_filename, sig_filename_len, "%s%s", payload->destfile_name, sig_suffix);
-				move_file(sig_filename, localpath);
+				move_file(sig_filename, localpath, user);
 				FREE(sig_filename);
 			}
 		}
@@ -1170,7 +1174,7 @@ static void prepare_resumable_downloads(alpm_list_t *payloads, const char *local
 			FREE(src);
 			continue;
 		}
-		if(pw != NULL) {
+		if(pw != NULL && pw->pw_uid != 0) {
 			ASSERT(chown(payload->tempfile_name, pw->pw_uid, pw->pw_gid), return);
 		}
 		FREE(src);
@@ -1267,7 +1271,7 @@ download_signature:
 		ret = updated ? 0 : 1;
 	}
 
-	if (finalize_download_locations(payloads, localpath) != 0 && ret == 0) {
+	if (finalize_download_locations(payloads, localpath, handle->sandboxuser) != 0 && ret == 0) {
 		RET_ERR(handle, ALPM_ERR_RETRIEVE, -1);
 	}
 	return ret;