[PATCH 6.6 111/567] scsi: target: Fix recursive locking in __configfs_open_file()

Greg Kroah-Hartman
2026-03-23T14:56:49Z

6.6-stable review patch. If anyone has any objections, please let me know.

------------------

From: Prithvi Tambewagh <activprithvi@gmail.com>

commit 14d4ac19d1895397532eec407433c5d74d9da53b upstream.

In flush_write_buffer, &p->frag_sem is acquired and then the loaded store
function is called, which, here, is target_core_item_dbroot_store(). This
function called filp_open(), following which these functions were called
(in reverse order), according to the call trace:

down_read
__configfs_open_file
do_dentry_open
vfs_open
do_open
path_openat
do_filp_open
file_open_name
filp_open
target_core_item_dbroot_store
flush_write_buffer
configfs_write_iter

target_core_item_dbroot_store() tries to validate the new file path by
trying to open the file path provided to it; however, in this case, the bug
report shows:

db_root: not a directory: /sys/kernel/config/target/dbroot

indicating that the same configfs file was tried to be opened, on which it
is currently working on. Thus, it is trying to acquire frag_sem semaphore
of the same file of which it already holds the semaphore obtained in
flush_write_buffer(), leading to acquiring the semaphore in a nested manner
and a possibility of recursive locking.

Fix this by modifying target_core_item_dbroot_store() to use kern_path()
instead of filp_open() to avoid opening the file using filesystem-specific
function __configfs_open_file(), and further modifying it to make this fix
compatible.

Reported-by: syzbot+f6e8174215573a84b797@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=f6e8174215573a84b797
Tested-by: syzbot+f6e8174215573a84b797@syzkaller.appspotmail.com
Cc: stable@vger.kernel.org
Signed-off-by: Prithvi Tambewagh <activprithvi@gmail.com>
Reviewed-by: Dmitry Bogdanov <d.bogdanov@yadro.com>
Link: https://patch.msgid.link/20260216062002.61937-1-activprithvi@gmail.com
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/target/target_core_configfs.c | 15 ++++++---------
1 file changed, 6 insertions(+), 9 deletions(-)

--- a/drivers/target/target_core_configfs.c
+++ b/drivers/target/target_core_configfs.c
@@ -108,8 +108,8 @@ static ssize_t target_core_item_dbroot_s
const char *page, size_t count)
{
ssize_t read_bytes;
- struct file *fp;
ssize_t r = -EINVAL;
+ struct path path = {};

mutex_lock(&target_devices_lock);
if (target_devices) {
@@ -131,17 +131,14 @@ static ssize_t target_core_item_dbroot_s
db_root_stage[read_bytes - 1] = '\0';

/* validate new db root before accepting it */
- fp = filp_open(db_root_stage, O_RDONLY, 0);
- if (IS_ERR(fp)) {
+ r = kern_path(db_root_stage, LOOKUP_FOLLOW | LOOKUP_DIRECTORY, &path);
+ if (r) {
pr_err("db_root: cannot open: %s\n", db_root_stage);
+ if (r == -ENOTDIR)
+ pr_err("db_root: not a directory: %s\n", db_root_stage);
goto unlock;
}
- if (!S_ISDIR(file_inode(fp)->i_mode)) {
- filp_close(fp, NULL);
- pr_err("db_root: not a directory: %s\n", db_root_stage);
- goto unlock;
- }
- filp_close(fp, NULL);
+ path_put(&path);

strncpy(db_root, db_root_stage, read_bytes);
pr_debug("Target_Core_ConfigFS: db_root set to %s\n", db_root);