[pacman-dev] [PATCH] libalpm: Check cachedir access before re-creating

[David Phillips]

If users have mounted a filesystem such as sshfs or NFS that doesn't
allow root access by default for security reasons, _alpm_filecache_setup
will blindly try and re-create the components of the cachedir path,
eating EACCES (to be liek mkdir -p). Then, it will return this path as
if it is valid when it may not be readable by root, causing
alpm_check_downloadspace to trigger a FPE since it assumes the cachedir
is R/W and uses fsinfo which may be zero.

This patch adds a check before trying to re-create the cachedir in order
to determine if creating it will result in EACCES, and outputs a warning
if so. It also discards the current cachedir from being considered. This
causes a more meaningful and graceful failure than a FPE.
---
 lib/libalpm/util.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/lib/libalpm/util.c b/lib/libalpm/util.c
index d33eef2a..d4375593 100644
--- a/lib/libalpm/util.c
+++ b/lib/libalpm/util.c
@@ -849,12 +849,16 @@ const char *_alpm_filecache_setup(alpm_handle_t *handle)
 	for(i = handle->cachedirs; i; i = i->next) {
 		cachedir = i->data;
 		if(stat(cachedir, &buf) != 0) {
-			/* cache directory does not exist.... try creating it */
-			_alpm_log(handle, ALPM_LOG_WARNING, _("no %s cache exists, creating...\n"),
-					cachedir);
-			if(_alpm_makepath(cachedir) == 0) {
-				_alpm_log(handle, ALPM_LOG_DEBUG, "using cachedir: %s\n", cachedir);
-				return cachedir;
+			if (errno == EACCES) {
+				_alpm_log(handle, ALPM_LOG_WARNING, _("failed to stat %s: %s\n"), cachedir, strerror(errno));
+			} else {
+				/* cache directory does not exist.... try creating it */
+				_alpm_log(handle, ALPM_LOG_WARNING, _("no %s cache exists, creating...\n"),
+						cachedir);
+				if(_alpm_makepath(cachedir) == 0) {
+					_alpm_log(handle, ALPM_LOG_DEBUG, "using cachedir: %s\n", cachedir);
+					return cachedir;
+				}
 			}
 		} else if(!S_ISDIR(buf.st_mode)) {
 			_alpm_log(handle, ALPM_LOG_DEBUG,
-- 
2.20.1