mm/damon/dbgfs: check if rm_contexts input is for a real context

A user could write a name of a file under 'damon/' debugfs directory,
which is not a user-created context, to 'rm_contexts' file.  In the case,
'dbgfs_rm_context()' just assumes it's the valid DAMON context directory
only if a file of the name exist.  As a result, invalid memory access
could happen as below.  Fix the bug by checking if the given input is for
a directory.  This check can filter out non-context inputs because
directories under 'damon/' debugfs directory can be created via only
'mk_contexts' file.

This bug has found by syzbot[1].

[1] https://lore.kernel.org/damon/[email protected]/

Link: https://lkml.kernel.org/r/[email protected]
Fixes: 75c1c2b53c78 ("mm/damon/dbgfs: support multiple contexts")
Signed-off-by: SeongJae Park <[email protected]>
Reported-by: [email protected]
Cc: <[email protected]>	[5.15.x]
Signed-off-by: Andrew Morton <[email protected]>

0 files changed, 0 insertions, 0 deletions