Re: getopt_long_only bug

[Rich Felker <dalias@libc.org>]

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On Thu, Apr 26, 2018 at 12:46:31PM +0200, Szabolcs Nagy wrote:
> i got the following bug report:
> 
> $ cat a.c
> #include <stdio.h>
> #include <getopt.h>
> 
> int main()
> {
> 	struct option lo[] =
> 	{
> 		{"emit-relocs", no_argument, NULL, 'q'},
> 		{"qmagic", no_argument, NULL, 'Q'},
> 		{ 0 }
> 	};
> 
> 	int li = -1;
> 	char* a[] = { "", "-q", NULL };
> 	int c = getopt_long_only(2, a, "q", lo, &li);
> 
> 	printf("c=%c/%i\n", c, c);
> 
> 	return 0;
> }
> $ ./a.musl
> c=Q/81
> $ ./a.glibc
> c=q/113

OK, this is a weird corner case. Apparently when in longonly mode,
short options need to be counted in addition to long ones for
determining if a partial match is unique.

The attached patch should solve the problem. Any review/comments would
be helpful. It uses an ugly inline strstr of sorts, because to use
strstr we'd need to copy to a temp buffer, and we wouldn't even
benefit since the string being searched is so short (usually 1 byte,
at most 4). The only reason it's there at all is because we committed
to supporting multibyte option chars in getopt.c so getopt_long_only
needs to handle them consistently.

Rich

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diff --git a/src/misc/getopt_long.c b/src/misc/getopt_long.c
index 008b747..ddcef94 100644
--- a/src/misc/getopt_long.c
+++ b/src/misc/getopt_long.c
@@ -1,5 +1,7 @@
 #define _GNU_SOURCE
 #include <stddef.h>
+#include <stdlib.h>
+#include <limits.h>
 #include <getopt.h>
 #include <stdio.h>
 #include <string.h>
@@ -58,10 +60,10 @@ static int __getopt_long_core(int argc, char *const *argv, const char *optstring
 	{
 		int colon = optstring[optstring[0]=='+'||optstring[0]=='-']==':';
 		int i, cnt, match;
-		char *arg, *opt;
+		char *arg, *opt, *start = argv[optind]+1;
 		for (cnt=i=0; longopts[i].name; i++) {
 			const char *name = longopts[i].name;
-			opt = argv[optind]+1;
+			opt = start;
 			if (*opt == '-') opt++;
 			while (*opt && *opt != '=' && *opt == *name)
 				name++, opt++;
@@ -74,6 +76,17 @@ static int __getopt_long_core(int argc, char *const *argv, const char *optstring
 			}
 			cnt++;
 		}
+		if (cnt==1 && longonly && arg-start == mblen(start, MB_LEN_MAX)) {
+			int l = arg-start;
+			for (i=0; optstring[i]; i++) {
+				int j;
+				for (j=0; j<l && start[j]==optstring[i+j]; j++);
+				if (j==l) {
+					cnt++;
+					break;
+				}
+			}
+		}
 		if (cnt==1) {
 			i = match;
 			opt = arg;