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

1 files changed, 15 insertions, 2 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,