setcap: clean up error handling of the ns rootid argument.

Bug reported by Artem S. Tashkinov:

   https://bugzilla.kernel.org/show_bug.cgi?id=214909

Signed-off-by: Andrew G. Morgan <morgan@kernel.org>

1 files changed, 33 insertions, 8 deletions

diff --git a/progs/setcap.c b/progs/setcap.c
index f8be53a..02a8a5d 100644
--- a/progs/setcap.c
+++ b/progs/setcap.c
@@ -26,13 +26,42 @@ static void usage(int status)
 	    " -h          this message and exit status 0\n"
 	    " -q          quietly\n"
 	    " -v          validate supplied capability matches file\n"
-	    " -n <rootid> write a user namespace limited capability\n"
+	    " -n <rootid> write a user namespace (!= 0) limited capability\n"
 	    " --license   display the license info\n"
 	);
     exit(status);
 }
 
-#define MAXCAP  2048
+/* parse a positive integer with some error handling */
+static unsigned long pos_uint(const char *text, const char *prefix, int *ok)
+{
+    char *remains;
+    unsigned long value;
+    ssize_t len = strlen(text);
+
+    if (len == 0 || *text == '-') {
+	goto fail;
+    }
+    value = strtoul(text, &remains, 0);
+    if (*remains || value == 0) {
+	goto fail;
+    }
+    if (ok != NULL) {
+	*ok = 1;
+    }
+    return value;
+
+fail:
+    if (ok == NULL) {
+	fprintf(stderr, "%s: want positive integer, got \"%s\"\n",
+		prefix, text);
+	exit(1);
+    }
+    *ok = 0;
+    return 0;
+}
+
+#define MAXCAP 2048
 
 static int read_caps(int quiet, const char *filename, char *buffer)
 {
@@ -99,7 +128,7 @@ int main(int argc, char **argv)
 	if (!strcmp("--license", *argv)) {
 	    printf(
 		"%s see LICENSE file for details.\n"
-		"Copyright (c) 1997,2007-8,2020,21 Andrew G. Morgan"
+		"Copyright (c) 1997,2007-8,2020-21 Andrew G. Morgan"
 		" <morgan@kernel.org>\n", argv[0]);
 	    exit(0);
 	}
@@ -117,11 +146,7 @@ int main(int argc, char **argv)
 		exit(1);
 	    }
 	    --argc;
-	    rootid = (uid_t) atoi(*++argv);
-	    if (rootid+1 < 2) {
-		fprintf(stderr, "invalid rootid!=0 of '%s'", *argv);
-		exit(1);
-	    }
+	    rootid = (uid_t) pos_uint(*++argv, "bad ns rootid", NULL);
 	    continue;
 	}