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vc_screen: don't clobber return value in vcs_read

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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>
This commit is contained in:
Thomas Weißschuh 2023-02-20 06:46:12 +00:00 • committed by Greg Kroah-Hartman
commit 465ce31a2b
1 changed files with 4 additions and 3 deletions
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7
drivers/tty/vt/vc_screen.c
View file

@ -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