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

Hence ultimately, __configfs_open_file() was called, indirectly by target_core_item_dbroot_store(), and it also attempted to acquire &p->frag_sem, which was already held by the same thread, acquired earlier in flush_write_buffer. This poses a possibility of recursive locking, which triggers the lockdep warning.

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 --- drivers/target/target_core_configfs.c | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/drivers/target/target_core_configfs.c b/drivers/target/target_core_configfs.c index b19acd662726..f29052e6a87d 100644 --- 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_store(struct config_item *item, 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 +131,18 @@ static ssize_t target_core_item_dbroot_store(struct config_item *item, 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, &path); + if (r) { pr_err("db_root: cannot open: %s\n", db_root_stage); goto unlock; } - if (!S_ISDIR(file_inode(fp)->i_mode)) { - filp_close(fp, NULL); + if (!d_is_dir(path.dentry)) { + path_put(&path); pr_err("db_root: not a directory: %s\n", db_root_stage); + r = -ENOTDIR; goto unlock; } - filp_close(fp, NULL); + path_put(&path);

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

base-commit: 3a8660878839faadb4f1a6dd72c3179c1df56787