validate %FILEPATH% when parsing repo dbs

Currently we make no effort to validate the %FILENAME% field in the
repo db. This allows for relative paths to be considered valid.

A carefully crafted db entry with a malicious relative path,
(e.g. `../../../../etc/passwd`) will cause pacman to to
overwrite _any_ file on the target's machine.

Add the following validation:

- doesn't start with '.'
- doesn't contain a '/'
- won't overflow PATH_MAX

Signed-off-by: Simon Gomizelj <simongmzlj@gmail.com>
Signed-off-by: Allan McRae <allan@archlinux.org>

1 files changed, 30 insertions, 0 deletions

diff --git a/lib/libalpm/be_sync.c b/lib/libalpm/be_sync.c
index 1cbe055e..f9fd5d1f 100644
--- a/lib/libalpm/be_sync.c
+++ b/lib/libalpm/be_sync.c
@@ -479,6 +479,33 @@ cleanup:
 	return count;
 }
 
+/* This function validates %FILENAME%. filename must be between 3 and
+ * PATH_MAX characters and cannot be contain a path */
+static int _alpm_validate_filename(alpm_db_t *db, const char *pkgname,
+		const char *filename)
+{
+	size_t len = strlen(filename);
+
+	if(filename[0] == '.') {
+		errno = EINVAL;
+		_alpm_log(db->handle, ALPM_LOG_ERROR, _("%s database is inconsistent: filename "
+					"of package %s is illegal\n"), db->treename, pkgname);
+		return -1;
+	} else if(memchr(filename, '/', len) != NULL) {
+		errno = EINVAL;
+		_alpm_log(db->handle, ALPM_LOG_ERROR, _("%s database is inconsistent: filename "
+					"of package %s is illegal\n"), db->treename, pkgname);
+		return -1;
+	} else if(len > PATH_MAX) {
+		errno = EINVAL;
+		_alpm_log(db->handle, ALPM_LOG_ERROR, _("%s database is inconsistent: filename "
+					"of package %s is too long\n"), db->treename, pkgname);
+		return -1;
+	}
+
+	return 0;
+}
+
 #define READ_NEXT() do { \
 	if(_alpm_archive_fgets(archive, &buf) != ARCHIVE_OK) goto error; \
 	line = buf.line; \
@@ -558,6 +585,9 @@ static int sync_db_read(alpm_db_t *db, struct archive *archive,
 				}
 			} else if(strcmp(line, "%FILENAME%") == 0) {
 				READ_AND_STORE(pkg->filename);
+				if(_alpm_validate_filename(db, pkg->name, pkg->filename) < 0) {
+					return -1;
+				}
 			} else if(strcmp(line, "%DESC%") == 0) {
 				READ_AND_STORE(pkg->desc);
 			} else if(strcmp(line, "%GROUPS%") == 0) {