libc: check name in getvent()/putenv()

passing "", "." or ".." as name caused a crash in
getenv() as it would open the directory; then seek()
to determine the file size would fail and return -1.

now checking for these special names and set
error string when its bad.

doing a single read() will not work when /env has a
9p fileserver mounted onto it and the file size is bigger
than the i/o unit. so doing incremental reads until
we get eof.

1 files changed, 8 insertions, 8 deletions

diff --git a/sys/src/libc/9sys/putenv.c b/sys/src/libc/9sys/putenv.c
index de2389482..a99aaeb5f 100644
--- a/sys/src/libc/9sys/putenv.c
+++ b/sys/src/libc/9sys/putenv.c
@@ -4,20 +4,20 @@
 int
 putenv(char *name, char *val)
 {
-	int f;
 	char ename[100];
-	long s;
+	int f, n;
 
-	if(strchr(name, '/') != nil)
-		return -1;
-	snprint(ename, sizeof ename, "/env/%s", name);
-	if(strcmp(ename+5, name) != 0)
+	if(name[0]=='\0' || strcmp(name, ".")==0 || strcmp(name, "..")==0 || strchr(name, '/')!=nil
+	|| strlen(name) >= sizeof(ename)-5){
+		werrstr("bad env name: %s", name);
 		return -1;
+	}
+	snprint(ename, sizeof(ename), "/env/%s", name);
 	f = create(ename, OWRITE, 0664);
 	if(f < 0)
 		return -1;
-	s = strlen(val);
-	if(write(f, val, s) != s){
+	n = strlen(val);
+	if(write(f, val, n) != n){
 		close(f);
 		return -1;
 	}