[pacman-dev] [PATCH v2] pacman: fix possible buffer overflow

[morganamilo]

in the function query_fileowner, if the user enters a string longer
than PATH_MAX then rpath will buffer overflow when lrealpath tries to
strcat everything together.

So make sure to bail early if the generated path is going to be bigger
than PATH_MAX.

This also fixes the compiler warning:
query.c: In function ‘query_fileowner’:
query.c:192:4: warning: ‘strncpy’ specified bound 4096 equals destination size [-Wstringop-truncation]
    strncpy(rpath, filename, PATH_MAX);

Signed-off-by: morganamilo <morganamilo at gmail.com>

diff --git a/src/pacman/query.c b/src/pacman/query.c
index 00c39638..c661fafb 100644
--- a/src/pacman/query.c
+++ b/src/pacman/query.c
@@ -102,7 +102,7 @@ static char *lrealpath(const char *path, char *resolved_path)
 {
 	const char *bname = mbasename(path);
 	char *rpath = NULL, *dname = NULL;
-	int success = 0;
+	int success = 0, len;
 
 	if(strcmp(bname, ".") == 0 || strcmp(bname, "..") == 0) {
 		/* the entire path needs to be resolved */
@@ -115,8 +115,14 @@ static char *lrealpath(const char *path, char *resolved_path)
 	if(!(rpath = realpath(dname, NULL))) {
 		goto cleanup;
 	}
+
+	len = strlen(rpath) + strlen(bname) + 2;
+	if (len > PATH_MAX) {
+		errno = ENAMETOOLONG;
+		goto cleanup;
+	}
 	if(!resolved_path) {
-		if(!(resolved_path = malloc(strlen(rpath) + strlen(bname) + 2))) {
+		if(!(resolved_path = malloc(len))) {
 			goto cleanup;
 		}
 	}
@@ -187,11 +193,16 @@ static int query_fileowner(alpm_list_t *targets)
 			}
 		}
 
+		errno = 0;
 		if(!lrealpath(filename, rpath)) {
+			if (errno == ENAMETOOLONG) {
+				pm_printf(ALPM_LOG_ERROR, _("path too long: %s/\n"), filename);
+				goto targcleanup;
+			}
 			/* Can't canonicalize path, try to proceed anyway */
-			strncpy(rpath, filename, PATH_MAX);
+			strncpy(rpath, filename, PATH_MAX - 1);
+			rpath[PATH_MAX - 1] = '\0';
 		}
-
 		if(strncmp(rpath, root, rootlen) != 0) {
 			/* file is outside root, we know nothing can own it */
 			pm_printf(ALPM_LOG_ERROR, _("No package owns %s\n"), filename);
-- 
2.19.0