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@vger.kernel.org Link: https://lore.kernel.org/r/ee3ec63269b43b34e1c90dd8c9743bf8@finder.org Fixes: 8d1b43f6a6df ("tty: Restrict access to TIOCLINUX' copy-and-paste subcommands") Signed-off-by: Günther Noack gnoack@google.com --- Changes in V2:
* Removed comment in vt.c (per Greg's suggestion)
* CC'd stable@
* I *kept* the CAP_SYS_ADMIN check *after* copy_from_user(), with the reasoning that:
1. I do not see a good alternative to reorder the code here. We need the data from copy_from_user() in order to know whether the CAP_SYS_ADMIN check even needs to be performed. 2. A previous get_user() from an adjacent memory region already worked (making this a very unlikely failure)
I would still appreciate a more formal Tested-by from Hanno (hint, hint) :)
--- drivers/tty/vt/selection.c | 14 ++++++++++++++ drivers/tty/vt/vt.c | 2 -- 2 files changed, 14 insertions(+), 2 deletions(-)
diff --git a/drivers/tty/vt/selection.c b/drivers/tty/vt/selection.c index 564341f1a74f..0bd6544e30a6 100644 --- a/drivers/tty/vt/selection.c +++ b/drivers/tty/vt/selection.c @@ -192,6 +192,20 @@ int set_selection_user(const struct tiocl_selection __user *sel, if (copy_from_user(&v, sel, sizeof(*sel))) 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); }
diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c index 96842ce817af..be5564ed8c01 100644 --- a/drivers/tty/vt/vt.c +++ b/drivers/tty/vt/vt.c @@ -3345,8 +3345,6 @@ int tioclinux(struct tty_struct *tty, unsigned long arg)
switch (type) { case TIOCL_SETSEL: - if (!capable(CAP_SYS_ADMIN)) - return -EPERM; return set_selection_user(param, tty); case TIOCL_PASTESEL: if (!capable(CAP_SYS_ADMIN))