[PATCH v2] mm/damon/dbgfs: avoid duplicate context directory creation

SeongJae Park
2022-08-19T17:49:58Z

From: Badari Pulavarty <badari.pulavarty@intel.com>

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 silently fails but the context is added in the
internal data structure. 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

This commit fixes the issue by checking if the name already exist and
immediately returning '-EEXIST' in the case.

Fixes: 75c1c2b53c78 ("mm/damon/dbgfs: support multiple contexts")
Cc: <stable@vger.kernel.org> # 5.15.x
Signed-off-by: Badari Pulavarty <badari.pulavarty@intel.com>
Signed-off-by: SeongJae Park <sj@kernel.org>
---
Changes from v1
(https://lore.kernel.org/damon/DM6PR11MB3978994F75A4104D714437379C679@DM6PR11MB3978.namprd11.prod.outlook.com/)
- Manually check duplicate entry instead of checking
'debugfs_create_dir()' return value
- Reword commit message and the test case

Seems Badari have some email client issue, so I (SJ) am making this
second version of the patch based on Badari's final proposal and repost
on behalf of Badari.

mm/damon/dbgfs.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/mm/damon/dbgfs.c b/mm/damon/dbgfs.c
index 51d67c8050dd..364b44063c2f 100644
--- a/mm/damon/dbgfs.c
+++ b/mm/damon/dbgfs.c
@@ -795,7 +795,7 @@ static void dbgfs_destroy_ctx(struct damon_ctx *ctx)
*/
static int dbgfs_mk_context(char *name)
{
- struct dentry *root, **new_dirs, *new_dir;
+ struct dentry *root, **new_dirs, *new_dir, *dir;
struct damon_ctx **new_ctxs, *new_ctx;

if (damon_nr_running_ctxs())
@@ -817,6 +817,12 @@ static int dbgfs_mk_context(char *name)
if (!root)
return -ENOENT;

+ dir = debugfs_lookup(name, root);
+ if (dir) {
+ dput(dir);
+ return -EEXIST;
+ }
+
new_dir = debugfs_create_dir(name, root);
dbgfs_dirs[dbgfs_nr_ctxs] = new_dir;

--
2.25.1