From 74bbb9e8b93f6a1640ac6eb9b178e0c0a0debd37 Mon Sep 17 00:00:00 2001
From: Rick Macklem <rmacklem@FreeBSD.org>
Date: Sat, 9 Aug 2025 14:15:07 -0700
Subject: [PATCH] vfs_syscalls.c: Fix handling of offset args for
 copy_file_range

Commit 197997a broke handling of the offset
arguments to copy_file_range() when specified non-NULL.
The code fails to update the offsets and, as such, a loop like:

do {

   len = copy_file_range(infd, &inpos, outfd, &outpos,
      SSIZE_MAX, 0);
} while (len > 0);

becomes an infinite loop, just doing the same copy over and
over again.

This patch fixes it.

The clause "(foffsets_locked || foffsets_set)" in the if is not
actually needed for correctness, but I thought it made the code
a little more readable and might avoid some static
analyzer from throwing a "used before being set" for
the savinoff and savoutoff variables.

Approved by:	so
Security:	FreeBSD-EN-25:16.vfs

(cherry picked from commit 4046ad6bb0ee542a42d89a48a7d6a56564ed7f33)
(cherry picked from commit 2fd0083fcc23f4c25860b8890292448720a5961c)
---
 sys/kern/vfs_syscalls.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/sys/kern/vfs_syscalls.c b/sys/kern/vfs_syscalls.c
index 02908f76ef8..6756925416a 100644
--- a/sys/kern/vfs_syscalls.c
+++ b/sys/kern/vfs_syscalls.c
@@ -4908,11 +4908,12 @@ kern_copy_file_range(struct thread *td, int infd, off_t *inoffp, int outfd,
 	size_t retlen;
 	void *rl_rcookie, *rl_wcookie;
 	off_t inoff, outoff, savinoff, savoutoff;
-	bool foffsets_locked;
+	bool foffsets_locked, foffsets_set;
 
 	infp = outfp = NULL;
 	rl_rcookie = rl_wcookie = NULL;
 	foffsets_locked = false;
+	foffsets_set = false;
 	error = 0;
 	retlen = 0;
 
@@ -4980,6 +4981,8 @@ kern_copy_file_range(struct thread *td, int infd, off_t *inoffp, int outfd,
 		}
 		foffset_lock_pair(infp1, &inoff, outfp1, &outoff, 0);
 		foffsets_locked = true;
+	} else {
+		foffsets_set = true;
 	}
 	savinoff = inoff;
 	savoutoff = outoff;
@@ -5035,11 +5038,12 @@ out:
 		vn_rangelock_unlock(invp, rl_rcookie);
 	if (rl_wcookie != NULL)
 		vn_rangelock_unlock(outvp, rl_wcookie);
+	if ((foffsets_locked || foffsets_set) &&
+	    (error == EINTR || error == ERESTART)) {
+		inoff = savinoff;
+		outoff = savoutoff;
+	}
 	if (foffsets_locked) {
-		if (error == EINTR || error == ERESTART) {
-			inoff = savinoff;
-			outoff = savoutoff;
-		}
 		if (inoffp == NULL)
 			foffset_unlock(infp, inoff, 0);
 		else
@@ -5048,6 +5052,9 @@ out:
 			foffset_unlock(outfp, outoff, 0);
 		else
 			*outoffp = outoff;
+	} else if (foffsets_set) {
+		*inoffp = inoff;
+		*outoffp = outoff;
 	}
 	if (outfp != NULL)
 		fdrop(outfp, td);