Revert r192094. The revision caused problems for sysctl(3) consumers

that expect that oldlen is filled with required buffer length even when
supplied buffer is too short and returned error is ENOMEM.

Redo the fix for kern.proc.filedesc, by reverting the req->oldidx when
remaining buffer space is too short for the current kinfo_file structure.
Also, only ignore ENOMEM. We have to convert ENOMEM to no error condition
to keep existing interface for the sysctl, though.

Reported by:	ed, Florian Smeets <flo kasimir com>
Tested by:	pho

2 files changed, 18 insertions, 7 deletions

diff --git a/sys/kern/kern_descrip.c b/sys/kern/kern_descrip.c
index f29b0eb..e0008e6 100644
--- a/sys/kern/kern_descrip.c
+++ b/sys/kern/kern_descrip.c
@@ -2883,6 +2883,7 @@ sysctl_kern_proc_filedesc(SYSCTL_HANDLER_ARGS)
 	struct proc *p;
 	struct tty *tp;
 	int vfslocked;
+	size_t oldidx;
 
 	name = (int *)arg1;
 	if ((p = pfind((pid_t)name[0])) == NULL)
@@ -3061,14 +3062,26 @@ sysctl_kern_proc_filedesc(SYSCTL_HANDLER_ARGS)
 		    strlen(kif->kf_path) + 1;
 		kif->kf_structsize = roundup(kif->kf_structsize,
 		    sizeof(uint64_t));
+		oldidx = req->oldidx;
 		error = SYSCTL_OUT(req, kif, kif->kf_structsize);
-		if (error)
+		if (error) {
+			if (error == ENOMEM) {
+				/*
+				 * The hack to keep the ABI of sysctl
+				 * kern.proc.filedesc intact, but not
+				 * to account a partially copied
+				 * kinfo_file into the oldidx.
+				 */
+				req->oldidx = oldidx;
+				error = 0;
+			}
 			break;
+		}
 	}
 	FILEDESC_SUNLOCK(fdp);
 	fddrop(fdp);
 	free(kif, M_TEMP);
-	return (0);
+	return (error);
 }
 
 static SYSCTL_NODE(_kern_proc, KERN_PROC_FILEDESC, filedesc, CTLFLAG_RD,
diff --git a/sys/kern/kern_sysctl.c b/sys/kern/kern_sysctl.c
index bf539be..0a8a096 100644
--- a/sys/kern/kern_sysctl.c
+++ b/sys/kern/kern_sysctl.c
@@ -1223,9 +1223,9 @@ sysctl_old_kernel(struct sysctl_req *req, const void *p, size_t l)
 		if (i > 0)
 			bcopy(p, (char *)req->oldptr + req->oldidx, i);
 	}
+	req->oldidx += l;
 	if (req->oldptr && i != l)
 		return (ENOMEM);
-	req->oldidx += l;
 	return (0);
 }
 
@@ -1322,10 +1322,9 @@ sysctl_old_user(struct sysctl_req *req, const void *p, size_t l)
 	size_t i, len, origidx;
 
 	origidx = req->oldidx;
-	if (req->oldptr == NULL) {
-		req->oldidx += l;
+	req->oldidx += l;
+	if (req->oldptr == NULL)
 		return (0);
-	}
 	/*
 	 * If we have not wired the user supplied buffer and we are currently
 	 * holding locks, drop a witness warning, as it's possible that
@@ -1347,7 +1346,6 @@ sysctl_old_user(struct sysctl_req *req, const void *p, size_t l)
 		return (error);
 	if (i < l)
 		return (ENOMEM);
-	req->oldidx += l;
 	return (0);
 }