unlink_file: strip trailing slashes

If the user replaces a directory with a symlink, libalpm would get
confused because the trailing slash causes system calls to resolve the
symlink.  This leads to errors and a misleading message during upgrades.
Even though libalpm does not support this, it should not be giving
misleading errors.

Also adds an overflow check.

Fixes FS#51377

Signed-off-by: Andrew Gregory <andrew.gregory.8@gmail.com>
(cherry picked from commit 16b91f798faf6413f9b043543c5c0c3467b6fdbf)

1 files changed, 12 insertions, 1 deletions

diff --git a/lib/libalpm/remove.c b/lib/libalpm/remove.c
index 173dbc69..ee8f288e 100644
--- a/lib/libalpm/remove.c
+++ b/lib/libalpm/remove.c
@@ -440,8 +440,19 @@ static int unlink_file(alpm_handle_t *handle, alpm_pkg_t *oldpkg,
 {
 	struct stat buf;
 	char file[PATH_MAX];
+	int file_len;
 
-	snprintf(file, PATH_MAX, "%s%s", handle->root, fileobj->name);
+	file_len = snprintf(file, PATH_MAX, "%s%s", handle->root, fileobj->name);
+	if(file_len <= 0 || file_len >= PATH_MAX) {
+		/* 0 is a valid value from snprintf, but should be impossible here */
+		_alpm_log(handle, ALPM_LOG_DEBUG, "path too long to unlink %s%s\n",
+				handle->root, fileobj->name);
+		return -1;
+	} else if(file[file_len-1] == '/') {
+		/* trailing slashes cause errors and confusing messages if the user has
+		 * replaced a directory with a symlink */
+		file[--file_len] = '\0';
+	}
 
 	if(llstat(file, &buf)) {
 		_alpm_log(handle, ALPM_LOG_DEBUG, "file %s does not exist\n", file);