In kvm_argv(), the case when the supplied buffer was too short to hold the

requested value was handled incorrectly, and the function retuned NULL
instead of the truncated result.

Fix this and also remove unnecessary check for buf != NULL, which alway
retuns true.

MFC after:	3 days

1 files changed, 31 insertions, 23 deletions

diff --git a/lib/libkvm/kvm_proc.c b/lib/libkvm/kvm_proc.c
index d32575c..dcf034c 100644
--- a/lib/libkvm/kvm_proc.c
+++ b/lib/libkvm/kvm_proc.c
@@ -658,30 +658,38 @@ kvm_argv(kvm_t *kd, const struct kinfo_proc *kp, int env, int nchr)
 			buflen = nchr;
 		}
 	}
-	if (buf != NULL) {
-		oid[0] = CTL_KERN;
-		oid[1] = KERN_PROC;
-		oid[2] = env ? KERN_PROC_ENV : KERN_PROC_ARGS;
-		oid[3] = kp->ki_pid;
-		bufsz = buflen;
-		i = sysctl(oid, 4, buf, &bufsz, 0, 0);
-		if (i == 0 && bufsz > 0) {
-			i = 0;
-			p = buf;
-			do {
-				bufp[i++] = p;
-				p += strlen(p) + 1;
-				if (i >= argc) {
-					argc += argc;
-					bufp = realloc(bufp,
-					    sizeof(char *) * argc);
-				}
-			} while (p < buf + bufsz);
-			bufp[i++] = 0;
-			return (bufp);
-		}
+	oid[0] = CTL_KERN;
+	oid[1] = KERN_PROC;
+	oid[2] = env ? KERN_PROC_ENV : KERN_PROC_ARGS;
+	oid[3] = kp->ki_pid;
+	bufsz = buflen;
+	if (sysctl(oid, 4, buf, &bufsz, 0, 0) == -1) {
+		/*
+		 * If the supplied buf is too short to hold the requested
+		 * value the sysctl returns with ENOMEM. The buf is filled
+		 * with the truncated value and the returned bufsz is equal
+		 * to the requested len.
+		 */
+		if (errno != ENOMEM || bufsz != (size_t)buflen)
+			return (0);
+		buf[bufsz - 1] = '\0';
+		errno = 0;
+	} else if (bufsz == 0) {
+		return (0);
 	}
-	return (NULL);
+	i = 0;
+	p = buf;
+	do {
+		bufp[i++] = p;
+		p += strlen(p) + 1;
+		if (i >= argc) {
+			argc += argc;
+			bufp = realloc(bufp,
+			    sizeof(char *) * argc);
+		}
+	} while (p < buf + bufsz);
+	bufp[i++] = 0;
+	return (bufp);
 }
 
 char **