From: SeongJae Park <sj@xxxxxxxxxx> commit 1de09a7281edecfdba19b3a07417f6d65243ab5f upstream. A user could write a name of a file under 'damon/' debugfs directory, which is not a user-created context, to 'rm_contexts' file. In the case, 'dbgfs_rm_context()' just assumes it's the valid DAMON context directory only if a file of the name exist. As a result, invalid memory access could happen as below. Fix the bug by checking if the given input is for a directory. This check can filter out non-context inputs because directories under 'damon/' debugfs directory can be created via only 'mk_contexts' file. This bug has found by syzbot[1]. [1] https://lore.kernel.org/damon/000000000000ede3ac05ec4abf8e@xxxxxxxxxx/ Link: https://lkml.kernel.org/r/20221107165001.5717-2-sj@xxxxxxxxxx Fixes: 75c1c2b53c78 ("mm/damon/dbgfs: support multiple contexts") Signed-off-by: SeongJae Park <sj@xxxxxxxxxx> Reported-by: syzbot+6087eafb76a94c4ac9eb@xxxxxxxxxxxxxxxxxxxxxxxxx Cc: <stable@xxxxxxxxxxxxxxx> [5.15.x] Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- mm/damon/dbgfs.c | 7 +++++++ 1 file changed, 7 insertions(+) --- a/mm/damon/dbgfs.c +++ b/mm/damon/dbgfs.c @@ -882,6 +882,7 @@ out: static int dbgfs_rm_context(char *name) { struct dentry *root, *dir, **new_dirs; + struct inode *inode; struct damon_ctx **new_ctxs; int i, j; int ret = 0; @@ -897,6 +898,12 @@ static int dbgfs_rm_context(char *name) if (!dir) return -ENOENT; + inode = d_inode(dir); + if (!S_ISDIR(inode->i_mode)) { + ret = -EINVAL; + goto out_dput; + } + new_dirs = kmalloc_array(dbgfs_nr_ctxs - 1, sizeof(*dbgfs_dirs), GFP_KERNEL); if (!new_dirs) {
