Commit 465ce31a authored Feb 20, 2023 by Thomas Weißschuh Committed by Greg Kroah-Hartman Mar 03, 2023

vc_screen: don't clobber return value in vcs_read



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 Weißschuh <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>

parent ee8cd3ab

drivers/tty/vt/vc_screen.c

+4 −3

Original line number	Diff line number	Diff line
		@@ -284,10 +284,11 @@ vcs_read(struct file file, char __user buf, size_t count, loff_t *ppos)
		ssize_t orig_count;
		long p = pos;

		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