mm/damon/dbgfs: avoid duplicate context directory creation

BugLink: https://bugs.launchpad.net/bugs/1991717
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>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/mm/damon/dbgfs.c b/mm/damon/dbgfs.c
index 36624990b577776b9bd78308bc2df90afcbb227d..70a5cb977ed0e4eea11bddc361e36057066eff78 100644 (file)
--- a/mm/damon/dbgfs.c
+++ b/mm/damon/dbgfs.c
@@ -376,6 +376,9 @@ 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();