mm/damon/dbgfs: avoid duplicate context directory creation

commit d26f60703606ab425eee9882b32a1781a8bed74d upstream.

When user tries to create a DAMON context via the DAMON debugfs interface
with a name of an already existing context, the context directory creation
fails but a new context is created and added in the internal data
structure, due to absence of the directory creation success check.  As a
result, memory could leak and DAMON cannot be turned on.  An example test
case is as below:

    # cd /sys/kernel/debug/damon/
    # echo "off" >  monitor_on
    # echo paddr > target_ids
    # echo "abc" > mk_context
    # echo "abc" > mk_context
    # echo $$ > abc/target_ids
    # echo "on" > monitor_on  <<< fails

Return value of 'debugfs_create_dir()' is expected to be ignored in
general, but this is an exceptional case as DAMON feature is depending
on the debugfs functionality and it has the potential duplicate name
issue.  This commit therefore fixes the issue by checking the directory
creation failure and immediately return the error in the case.

Link: https://lkml.kernel.org/r/20220821180853.2400-1-sj@kernel.org
Fixes: 75c1c2b53c78 ("mm/damon/dbgfs: support multiple contexts")
Signed-off-by: Badari Pulavarty <badari.pulavarty@intel.com>
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: <stable@vger.kernel.org>	[ 5.15.x]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/mm/damon/dbgfs.c b/mm/damon/dbgfs.c
index a0dab8b5e45f2fbf8fb700160c5f8913d79ef1bd..53ba8b1e619ca3b2c3a08d4debeca8d409ac62a0 100644 (file)
--- a/mm/damon/dbgfs.c
+++ b/mm/damon/dbgfs.c
@@ -787,6 +787,9 @@ static int dbgfs_mk_context(char *name)
                return -ENOENT;
 
        new_dir = debugfs_create_dir(name, root);
+       /* Below check is required for a potential duplicated name case */
+       if (IS_ERR(new_dir))
+               return PTR_ERR(new_dir);
        dbgfs_dirs[dbgfs_nr_ctxs] = new_dir;
 
        new_ctx = dbgfs_new_ctx();