7.3-stable review patch. If anyone has any objections, please let me know. ------------------ From: Yongjun Gwon commit 7220980b2423d06a0604516129bfa4cec8a697ae upstream. SMB2 QUERY_DIRECTORY holds fp->readdir_lock while it calls iterate_dir() on fp->filp. An SMB2 SET_INFO request with FILE_DISPOSITION_INFORMATION can resolve the same FileId and call ksmbd_vfs_empty_dir() on the same filp without that lock. iterate_dir()'s inode read lock permits concurrent readers and does not serialize per-file iterator state. ext4 stores its dx readdir cursor and fname RB tree in file->private_data. Concurrent reset or refill can therefore free a fname node while the other worker still traverses it or retains its RB-tree link, resulting in use-after-free accesses. An authenticated SMB client with list and delete rights on a directory in a writable KSMBD share backed by ext4 can trigger this when the directory takes the dx readdir path. The client overlaps an SMB2 QUERY_DIRECTORY request with an SMB2 SET_INFO request carrying FILE_DISPOSITION_INFORMATION on one live FileId. In one x86_64 SMP KASAN multi-shot guest using ksmbd-for-next at 171df27077fb, the unmodified kernel reported a cross-worker use-after-free before a panic. The first report's access and free stacks show the two request paths directly (trimmed): BUG: KASAN: slab-use-after-free in ext4_htree_store_dirent+0x488/0x550 Read of size 8 by task kworker/2:0/29 Workqueue: ksmbd-io handle_ksmbd_work Call Trace: ext4_htree_store_dirent+0x488/0x550 htree_dirblock_to_tree+0x535/0x990 ext4_htree_fill_tree+0x319/0xba0 ext4_readdir+0x175a/0x2f40 iterate_dir+0x1b6/0x630 smb2_query_dir+0x1003/0x1cc0 Freed by task 279: free_rb_tree_fname+0x67/0xc0 ext4_readdir+0x13a9/0x2f40 iterate_dir+0x1b6/0x630 ksmbd_vfs_empty_dir+0xa2/0x100 smb2_set_info+0x2ffa/0x45d0 Take fp->readdir_lock across the entire emptiness check. This places both iterators over that handle's filp in the same lock domain while preserving the disposition status handling. The exact code change completed a warning-free x86_64 KASAN bzImage build. Tracing three request pairs showed that the two iterate_dir() calls no longer overlapped and the expected statuses were preserved. A further 1,600 reproducer iterations completed with expected statuses and no KASAN report, Oops, or panic. The reproducer and complete guest configuration are available privately to maintainers on request. Fixes: e2f34481b24d ("cifsd: add server-side procedures for SMB3") Cc: stable@vger.kernel.org Assisted-by: LLM Signed-off-by: Yongjun Gwon Signed-off-by: Namjae Jeon Signed-off-by: Greg Kroah-Hartman --- fs/smb/server/smb2pdu.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) --- a/fs/smb/server/smb2pdu.c +++ b/fs/smb/server/smb2pdu.c @@ -8324,6 +8324,7 @@ static int set_file_disposition_info(str struct smb2_file_disposition_info *file_info) { struct inode *inode; + int err; if (!(fp->daccess & FILE_DELETE_LE)) { pr_err("no right to delete : 0x%x\n", fp->daccess); @@ -8338,9 +8339,13 @@ static int set_file_disposition_info(str if (ksmbd_has_stream_without_delete_share(fp)) return -ESHARE; - if (S_ISDIR(inode->i_mode) && !ksmbd_stream_fd(fp) && - ksmbd_vfs_empty_dir(fp) == -ENOTEMPTY) - return -EBUSY; + if (S_ISDIR(inode->i_mode) && !ksmbd_stream_fd(fp)) { + mutex_lock(&fp->readdir_lock); + err = ksmbd_vfs_empty_dir(fp); + mutex_unlock(&fp->readdir_lock); + if (err == -ENOTEMPTY) + return -EBUSY; + } smb_break_all_levII_oplock_for_delete(work, fp); ksmbd_fd_set_delete_pending(fp); } else {