Re: [PATCH v3] mm/damon/dbgfs: avoid duplicate context directory creation

On Sun, Aug 21, 2022 at 06:08:53PM +0000, SeongJae Park wrote:

From: Badari Pulavarty badari.pulavarty@intel.com

From: Badari Pulavarty badari.pulavarty@intel.com

Twice?

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.

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 v2 (https://lore.kernel.org/damon/20220819171930.16166-1-sj@kernel.org/)

• Simply check the debugfs_create_dir() return value (Andrew Morton)
• Put a comment for justifying check of the return value (Greg KH)

Changes from v1 (https://lore.kernel.org/damon/DM6PR11MB3978994F75A4104D714437379C679@DM6PR11...)

• 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 third version of the patch based on Badari's final proposal and reposting on behalf of Badari.

mm/damon/dbgfs.c | 3 +++ 1 file changed, 3 insertions(+)

diff --git a/mm/damon/dbgfs.c b/mm/damon/dbgfs.c index 51d67c8050dd..3b55a1b219b5 100644 --- a/mm/damon/dbgfs.c +++ b/mm/damon/dbgfs.c @@ -818,6 +818,9 @@ 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);
  

Did you just leak the memory allocated above this check? It's hard to determine as you are setting global variables.

thanks,

greg k-h