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tty: Permit some TIOCL_SETSEL modes without CAP_SYS_ADMIN

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With this, processes without CAP_SYS_ADMIN are able to use TIOCLINUX with
subcode TIOCL_SETSEL, in the selection modes TIOCL_SETPOINTER,
TIOCL_SELCLEAR and TIOCL_SELMOUSEREPORT.

TIOCL_SETSEL was previously changed to require CAP_SYS_ADMIN, as this IOCTL
let callers change the selection buffer and could be used to simulate
keypresses.  These three TIOCL_SETSEL selection modes, however, are safe to
use, as they do not modify the selection buffer.

This fixes a mouse support regression that affected Emacs (invisible mouse
cursor).

Cc: stable <stable@kernel.org>
Link: https://lore.kernel.org/r/ee3ec63269b43b34e1c90dd8c9743bf8@finder.org
Fixes: 8d1b43f6a6 ("tty: Restrict access to TIOCLINUX' copy-and-paste subcommands")
Signed-off-by: Günther Noack <gnoack@google.com>
Reviewed-by: Kees Cook <kees@kernel.org>
Link: https://lore.kernel.org/r/20250110142122.1013222-1-gnoack@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Günther Noack 2025-01-10 14:21:22 +00:00 • committed by Greg Kroah-Hartman
parent b06f388994
commit 2f83e38a09
2 changed files with 14 additions and 2 deletions
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14
drivers/tty/vt/selection.c
View file

@ -192,6 +192,20 @@ int set_selection_user(const struct tiocl_selection __user *sel,
if (copy_from_user(&v, sel, sizeof(*sel))) if (copy_from_user(&v, sel, sizeof(*sel)))
return -EFAULT; return -EFAULT;
/*
* TIOCL_SELCLEAR, TIOCL_SELPOINTER and TIOCL_SELMOUSEREPORT are OK to
* use without CAP_SYS_ADMIN as they do not modify the selection.
*/
switch (v.sel_mode) {
case TIOCL_SELCLEAR:
case TIOCL_SELPOINTER:
case TIOCL_SELMOUSEREPORT:
break;
default:
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
}
return set_selection_kernel(&v, tty); return set_selection_kernel(&v, tty);
} }

2
drivers/tty/vt/vt.c
View file

@ -3345,8 +3345,6 @@ int tioclinux(struct tty_struct *tty, unsigned long arg)
switch (type) { switch (type) {
case TIOCL_SETSEL: case TIOCL_SETSEL:
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
return set_selection_user(param, tty); return set_selection_user(param, tty);
case TIOCL_PASTESEL: case TIOCL_PASTESEL:
if (!capable(CAP_SYS_ADMIN)) if (!capable(CAP_SYS_ADMIN))