[pacman-dev] [PATCH] libalpm: never attempt to remove a mountpoint

[Dave Reisner]

Arch Linux typically runs into this with /sys when upgrading the
filesystem package in build chroots, but LXC users might also run into
this, since their /sys is shared from the host and must, for security
reasons, be mounted RO.

I've neglected to add any tests for this because they would require root
in order to run. Current tests all pass with this patch and I've
confirmed the desired behavior in a VM. Incidentally, the first hunk of
this patch (skipping can_remove_file checks for directories) resolves the
case of API mountpoints being removed since they eventually fall into
unlink_file and fail with "contains files". However, this patch should
still be the Right Thing To Do™, as we can't possibly remove a directory
that is also a mountpoint.

Signed-off-by: Dave Reisner <dreisner at archlinux.org>
---
This sort of addresses some of the concerns in FS#21971 and FS#30884, but
note that it doesn't actually deal with strictly read only filesystems.

 lib/libalpm/remove.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/lib/libalpm/remove.c b/lib/libalpm/remove.c
index b965391..548102f 100644
--- a/lib/libalpm/remove.c
+++ b/lib/libalpm/remove.c
@@ -299,6 +299,22 @@ static int can_remove_file(alpm_handle_t *handle, const alpm_file_t *file,
 	return 1;
 }
 
+static int dir_is_mountpoint(alpm_handle_t *handle, const char *directory,
+		const struct stat *stbuf) {
+	char parent_dir[PATH_MAX];
+	struct stat parent_stbuf;
+
+	snprintf(parent_dir, PATH_MAX, "%s..", directory);
+	if(stat(parent_dir, &parent_stbuf) < 0) {
+		_alpm_log(handle, ALPM_LOG_DEBUG,
+				"failed to stat parent of %s: %s: %s",
+				directory, parent_dir, strerror(errno));
+		return 0;
+	}
+
+	return stbuf->st_dev != parent_stbuf.st_dev;
+}
+
 /**
  * @brief Unlink a package file, backing it up if necessary.
  *
@@ -352,6 +368,9 @@ static int unlink_file(alpm_handle_t *handle, alpm_pkg_t *oldpkg,
 					fileobj->name)) {
 			_alpm_log(handle, ALPM_LOG_DEBUG,
 					"keeping directory %s (in new package)\n", file);
+		} else if(dir_is_mountpoint(handle, file, &buf)) {
+			_alpm_log(handle, ALPM_LOG_DEBUG,
+					"keeping directory %s (mountpoint)\n", file);
 		} else {
 			/* one last check- does any other package own this file? */
 			alpm_list_t *local, *local_pkgs;
@@ -479,6 +498,10 @@ static int remove_package_files(alpm_handle_t *handle,
 	filelist = alpm_pkg_get_files(oldpkg);
 	for(i = 0; i < filelist->count; i++) {
 		alpm_file_t *file = filelist->files + i;
+		/* ignore directories */
+		if(file->name[strlen(file->name) - 1] == '/') {
+			continue;
+		}
 		if(!can_remove_file(handle, file, skip_remove)) {
 			_alpm_log(handle, ALPM_LOG_DEBUG,
 					"not removing package '%s', can't remove all files\n",
-- 
1.8.1