+ mm-damon-dbgfs-avoid-duplicate-context-directory-creation.patch added to mm-hotfixes-unstable branch

+ mm-damon-dbgfs-avoid-duplicate-context-directory-creation.patch added to mm-hotfixes-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm/damon/dbgfs: avoid duplicate context directory creation
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     mm-damon-dbgfs-avoid-duplicate-context-directory-creation.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-damon-dbgfs-avoid-duplicate-context-directory-creation.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days

------------------------------------------------------
From: Badari Pulavarty <badari.pulavarty@intel.com>
Subject: mm/damon/dbgfs: avoid duplicate context directory creation
Date: Sun, 21 Aug 2022 18:08:53 +0000

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>
---

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

--- a/mm/damon/dbgfs.c~mm-damon-dbgfs-avoid-duplicate-context-directory-creation
+++ a/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);
 	dbgfs_dirs[dbgfs_nr_ctxs] = new_dir;
 
 	new_ctx = dbgfs_new_ctx();
_

Patches currently in -mm which might be from badari.pulavarty@intel.com are

mm-damon-dbgfs-avoid-duplicate-context-directory-creation.patch