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From: =?UTF-8?q?Thomas=20Wei=C3=9Fschuh?= <linux@weissschuh.net>
Date: Mon, 20 Feb 2023 06:46:12 +0000
Subject: [PATCH] vc_screen: don't clobber return value in vcs_read
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References: bsc#1012628
Patch-mainline: 6.2.2
Git-commit: ae3419fbac845b4d3f3a9fae4cc80c68d82cdf6e

commit ae3419fbac845b4d3f3a9fae4cc80c68d82cdf6e upstream.

Commit 226fae124b2d ("vc_screen: move load of struct vc_data pointer in
vcs_read() to avoid UAF") moved the call to vcs_vc() into the loop.

While doing this it also moved the unconditional assignment of

	ret = -ENXIO;

This unconditional assignment was valid outside the loop but within it
it clobbers the actual value of ret.

To avoid this only assign "ret = -ENXIO" when actually needed.

[ Also, the 'goto unlock_out" needs to be just a "break", so that it
  does the right thing when it exits on later iterations when partial
  success has happened - Linus ]

Reported-by: Storm Dragon <stormdragon2976@gmail.com>
Link: https://lore.kernel.org/lkml/Y%2FKS6vdql2pIsCiI@hotmail.com/
Fixes: 226fae124b2d ("vc_screen: move load of struct vc_data pointer in vcs_read() to avoid UAF")
Signed-off-by: Thomas WeiƟschuh <linux@weissschuh.net>
Link: https://lore.kernel.org/lkml/64981d94-d00c-4b31-9063-43ad0a384bde@t-8ch.de/
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
 drivers/tty/vt/vc_screen.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/tty/vt/vc_screen.c b/drivers/tty/vt/vc_screen.c
index f566eb18..71e091f8 100644
--- a/drivers/tty/vt/vc_screen.c
+++ b/drivers/tty/vt/vc_screen.c
@@ -403,10 +403,11 @@ vcs_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
 		unsigned int this_round, skip = 0;
 		int size;
 
-		ret = -ENXIO;
 		vc = vcs_vc(inode, &viewed);
-		if (!vc)
-			goto unlock_out;
+		if (!vc) {
+			ret = -ENXIO;
+			break;
+		}
 
 		/* Check whether we are above size each round,
 		 * as copy_to_user at the end of this loop
-- 
2.35.3