kernel/linux.git/fs/ceph/dir.c, branch v6.18.21

ceph: fix i_nlink underrun during async unlink

2026-03-19T15:08:30+00:00

commit ce0123cbb4a40a2f1bbb815f292b26e96088639f upstream. During async unlink, we drop the `i_nlink` counter before we receive the completion (that will eventually update the `i_nlink`) because "we assume that the unlink will succeed". That is not a bad idea, but it races against deletions by other clients (or against the completion of our own unlink) and can lead to an underrun which emits a WARNING like this one: WARNING: CPU: 85 PID: 25093 at fs/inode.c:407 drop_nlink+0x50/0x68 Modules linked in: CPU: 85 UID: 3221252029 PID: 25093 Comm: php-cgi8.1 Not tainted 6.14.11-cm4all1-ampere #655 Hardware name: Supermicro ARS-110M-NR/R12SPD-A, BIOS 1.1b 10/17/2023 pstate: 60400009 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--) pc : drop_nlink+0x50/0x68 lr : ceph_unlink+0x6c4/0x720 sp : ffff80012173bc90 x29: ffff80012173bc90 x28: ffff086d0a45aaf8 x27: ffff0871d0eb5680 x26: ffff087f2a64a718 x25: 0000020000000180 x24: 0000000061c88647 x23: 0000000000000002 x22: ffff07ff9236d800 x21: 0000000000001203 x20: ffff07ff9237b000 x19: ffff088b8296afc0 x18: 00000000f3c93365 x17: 0000000000070000 x16: ffff08faffcbdfe8 x15: ffff08faffcbdfec x14: 0000000000000000 x13: 45445f65645f3037 x12: 34385f6369706f74 x11: 0000a2653104bb20 x10: ffffd85f26d73290 x9 : ffffd85f25664f94 x8 : 00000000000000c0 x7 : 0000000000000000 x6 : 0000000000000002 x5 : 0000000000000081 x4 : 0000000000000481 x3 : 0000000000000000 x2 : 0000000000000000 x1 : 0000000000000000 x0 : ffff08727d3f91e8 Call trace: drop_nlink+0x50/0x68 (P) vfs_unlink+0xb0/0x2e8 do_unlinkat+0x204/0x288 __arm64_sys_unlinkat+0x3c/0x80 invoke_syscall.constprop.0+0x54/0xe8 do_el0_svc+0xa4/0xc8 el0_svc+0x18/0x58 el0t_64_sync_handler+0x104/0x130 el0t_64_sync+0x154/0x158 In ceph_unlink(), a call to ceph_mdsc_submit_request() submits the CEPH_MDS_OP_UNLINK to the MDS, but does not wait for completion. Meanwhile, between this call and the following drop_nlink() call, a worker thread may process a CEPH_CAP_OP_IMPORT, CEPH_CAP_OP_GRANT or just a CEPH_MSG_CLIENT_REPLY (the latter of which could be our own completion). These will lead to a set_nlink() call, updating the `i_nlink` counter to the value received from the MDS. If that new `i_nlink` value happens to be zero, it is illegal to decrement it further. But that is exactly what ceph_unlink() will do then. The WARNING can be reproduced this way: 1. Force async unlink; only the async code path is affected. Having no real clue about Ceph internals, I was unable to find out why the MDS wouldn't give me the "Fxr" capabilities, so I patched get_caps_for_async_unlink() to always succeed. (Note that the WARNING dump above was found on an unpatched kernel, without this kludge - this is not a theoretical bug.) 2. Add a sleep call after ceph_mdsc_submit_request() so the unlink completion gets handled by a worker thread before drop_nlink() is called. This guarantees that the `i_nlink` is already zero before drop_nlink() runs. The solution is to skip the counter decrement when it is already zero, but doing so without a lock is still racy (TOCTOU). Since ceph_fill_inode() and handle_cap_grant() both hold the `ceph_inode_info.i_ceph_lock` spinlock while set_nlink() runs, this seems like the proper lock to protect the `i_nlink` updates. I found prior art in NFS and SMB (using `inode.i_lock`) and AFS (using `afs_vnode.cb_lock`). All three have the zero check as well. Cc: stable@vger.kernel.org Fixes: 2ccb45462aea ("ceph: perform asynchronous unlink if we have sufficient caps") Signed-off-by: Max Kellermann Reviewed-by: Viacheslav Dubeyko Signed-off-by: Ilya Dryomov Signed-off-by: Greg Kroah-Hartman

ceph: add a bunch of missing ceph_path_info initializers

2026-03-19T15:08:29+00:00

commit 43323a5934b660afae687e8e4e95ac328615a5c4 upstream. ceph_mdsc_build_path() must be called with a zero-initialized ceph_path_info parameter, or else the following ceph_mdsc_free_path_info() may crash. Example crash (on Linux 6.18.12): virt_to_cache: Object is not a Slab page! WARNING: CPU: 184 PID: 2871736 at mm/slub.c:6732 kmem_cache_free+0x316/0x400 [...] Call Trace: [...] ceph_open+0x13d/0x3e0 do_dentry_open+0x134/0x480 vfs_open+0x2a/0xe0 path_openat+0x9a3/0x1160 [...] cache_from_obj: Wrong slab cache. names_cache but object is from ceph_inode_info WARNING: CPU: 184 PID: 2871736 at mm/slub.c:6746 kmem_cache_free+0x2dd/0x400 [...] kernel BUG at mm/slub.c:634! Oops: invalid opcode: 0000 [#1] SMP NOPTI RIP: 0010:__slab_free+0x1a4/0x350 Some of the ceph_mdsc_build_path() callers had initializers, but others had not, even though they were all added by commit 15f519e9f883 ("ceph: fix race condition validating r_parent before applying state"). The ones without initializer are suspectible to random crashes. (I can imagine it could even be possible to exploit this bug to elevate privileges.) Unfortunately, these Ceph functions are undocumented and its semantics can only be derived from the code. I see that ceph_mdsc_build_path() initializes the structure only on success, but not on error. Calling ceph_mdsc_free_path_info() after a failed ceph_mdsc_build_path() call does not even make sense, but that's what all callers do, and for it to be safe, the structure must be zero-initialized. The least intrusive approach to fix this is therefore to add initializers everywhere. Cc: stable@vger.kernel.org Fixes: 15f519e9f883 ("ceph: fix race condition validating r_parent before applying state") Signed-off-by: Max Kellermann Reviewed-by: Viacheslav Dubeyko Signed-off-by: Ilya Dryomov Signed-off-by: Greg Kroah-Hartman

ceph: refactor wake_up_bit() pattern of calling

2025-10-08T21:30:46+00:00

The wake_up_bit() is called in ceph_async_unlink_cb(), wake_async_create_waiters(), and ceph_finish_async_create(). It makes sense to switch on clear_bit() function, because it makes the code much cleaner and easier to understand. More important rework is the adding of smp_mb__after_atomic() memory barrier after the bit modification and before wake_up_bit() call. It can prevent potential race condition of accessing the modified bit in other threads. Luckily, clear_and_wake_up_bit() already implements the required functionality pattern: static inline void clear_and_wake_up_bit(int bit, unsigned long *word) { clear_bit_unlock(bit, word); /* See wake_up_bit() for which memory barrier you need to use. */ smp_mb__after_atomic(); wake_up_bit(word, bit); } Signed-off-by: Viacheslav Dubeyko Reviewed-by: Alex Markuze Signed-off-by: Ilya Dryomov

ceph: fix race condition validating r_parent before applying state

2025-09-09T10:57:02+00:00

Add validation to ensure the cached parent directory inode matches the directory info in MDS replies. This prevents client-side race conditions where concurrent operations (e.g. rename) cause r_parent to become stale between request initiation and reply processing, which could lead to applying state changes to incorrect directory inodes. [ idryomov: folded a kerneldoc fixup and a follow-up fix from Alex to move CEPH_CAP_PIN reference when r_parent is updated: When the parent directory lock is not held, req->r_parent can become stale and is updated to point to the correct inode. However, the associated CEPH_CAP_PIN reference was not being adjusted. The CEPH_CAP_PIN is a reference on an inode that is tracked for accounting purposes. Moving this pin is important to keep the accounting balanced. When the pin was not moved from the old parent to the new one, it created two problems: The reference on the old, stale parent was never released, causing a reference leak. A reference for the new parent was never acquired, creating the risk of a reference underflow later in ceph_mdsc_release_request(). This patch corrects the logic by releasing the pin from the old parent and acquiring it for the new parent when r_parent is switched. This ensures reference accounting stays balanced. ] Cc: stable@vger.kernel.org Signed-off-by: Alex Markuze Reviewed-by: Viacheslav Dubeyko Signed-off-by: Ilya Dryomov

ceph: fix a race with rename() in ceph_mdsc_build_path()

2025-06-17T21:58:14+00:00

Lift copying the name into callers of ceph_encode_encrypted_dname() that do not have it already copied; ceph_encode_encrypted_fname() disappears. That fixes a UAF in ceph_mdsc_build_path() - while the initial copy of plaintext into buf is done under ->d_lock, we access the original name again in ceph_encode_encrypted_fname() and that is done without any locking. With ceph_encode_encrypted_dname() using the stable copy the problem goes away. Tested-by: Viacheslav Dubeyko Reviewed-by: Viacheslav Dubeyko Signed-off-by: Al Viro

Merge tag 'vfs-6.15-rc1.ceph' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs

2025-03-24T19:17:13+00:00

Pull vfs ceph updates from Christian Brauner: "This contains the work to remove access to page->index from ceph and fixes the test failure observed for ceph with generic/421 by refactoring ceph_writepages_start()" * tag 'vfs-6.15-rc1.ceph' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs: fscrypt: Change fscrypt_encrypt_pagecache_blocks() to take a folio ceph: Fix error handling in fill_readdir_cache() fs: Remove page_mkwrite_check_truncate() ceph: Pass a folio to ceph_allocate_page_array() ceph: Convert ceph_move_dirty_page_in_page_array() to move_dirty_folio_in_page_array() ceph: Remove uses of page from ceph_process_folio_batch() ceph: Convert ceph_check_page_before_write() to use a folio ceph: Convert writepage_nounlock() to write_folio_nounlock() ceph: Convert ceph_readdir_cache_control to store a folio ceph: Convert ceph_find_incompatible() to take a folio ceph: Use a folio in ceph_page_mkwrite() ceph: Remove ceph_writepage() ceph: fix generic/421 test failure ceph: introduce ceph_submit_write() method ceph: introduce ceph_process_folio_batch() method ceph: extend ceph_writeback_ctl for ceph_writepages_start() refactoring

ceph: Convert ceph_readdir_cache_control to store a folio

2025-02-28T10:21:30+00:00

Pass a folio around instead of a page. This removes an access to page->index and a few hidden calls to compound_head(). Signed-off-by: "Matthew Wilcox (Oracle)" Link: https://lore.kernel.org/r/20250217185119.430193-5-willy@infradead.org Tested-by: Viacheslav Dubeyko Reviewed-by: Viacheslav Dubeyko Signed-off-by: Christian Brauner

ceph: return the correct dentry on mkdir

2025-02-27T19:00:17+00:00

ceph already splices the correct dentry (in splice_dentry()) from the result of mkdir but does nothing more with it. Now that ->mkdir can return a dentry, return the correct dentry. Note that previously ceph_mkdir() could call ceph_init_inode_acls() on the inode from the wrong dentry, which would be NULL. This is safe as ceph_init_inode_acls() checks for NULL, but is not strictly correct. With this patch, the inode for the returned dentry is passed to ceph_init_inode_acls(). Reviewed-by: Viacheslav Dubeyko Signed-off-by: NeilBrown Link: https://lore.kernel.org/r/20250227013949.536172-4-neilb@suse.de Signed-off-by: Christian Brauner

Change inode_operations.mkdir to return struct dentry *

2025-02-27T19:00:17+00:00

Some filesystems, such as NFS, cifs, ceph, and fuse, do not have complete control of sequencing on the actual filesystem (e.g. on a different server) and may find that the inode created for a mkdir request already exists in the icache and dcache by the time the mkdir request returns. For example, if the filesystem is mounted twice the directory could be visible on the other mount before it is on the original mount, and a pair of name_to_handle_at(), open_by_handle_at() calls could instantiate the directory inode with an IS_ROOT() dentry before the first mkdir returns. This means that the dentry passed to ->mkdir() may not be the one that is associated with the inode after the ->mkdir() completes. Some callers need to interact with the inode after the ->mkdir completes and they currently need to perform a lookup in the (rare) case that the dentry is no longer hashed. This lookup-after-mkdir requires that the directory remains locked to avoid races. Planned future patches to lock the dentry rather than the directory will mean that this lookup cannot be performed atomically with the mkdir. To remove this barrier, this patch changes ->mkdir to return the resulting dentry if it is different from the one passed in. Possible returns are: NULL - the directory was created and no other dentry was used ERR_PTR() - an error occurred non-NULL - this other dentry was spliced in This patch only changes file-systems to return "ERR_PTR(err)" instead of "err" or equivalent transformations. Subsequent patches will make further changes to some file-systems to return a correct dentry. Not all filesystems reliably result in a positive hashed dentry: - NFS, cifs, hostfs will sometimes need to perform a lookup of the name to get inode information. Races could result in this returning something different. Note that this lookup is non-atomic which is what we are trying to avoid. Placing the lookup in filesystem code means it only happens when the filesystem has no other option. - kernfs and tracefs leave the dentry negative and the ->revalidate operation ensures that lookup will be called to correctly populate the dentry. This could be fixed but I don't think it is important to any of the users of vfs_mkdir() which look at the dentry. The recommendation to use d_drop();d_splice_alias() is ugly but fits with current practice. A planned future patch will change this. Reviewed-by: Jeff Layton Reviewed-by: Jan Kara Signed-off-by: NeilBrown Link: https://lore.kernel.org/r/20250227013949.536172-2-neilb@suse.de Signed-off-by: Christian Brauner

ceph_d_revalidate(): propagate stable name down into request encoding

2025-01-28T00:25:23+00:00

Currently get_fscrypt_altname() requires ->r_dentry->d_name to be stable and it gets that in almost all cases. The only exception is ->d_revalidate(), where we have a stable name, but it's passed separately - dentry->d_name is not stable there. Propagate it down to get_fscrypt_altname() as a new field of struct ceph_mds_request - ->r_dname, to be used instead ->r_dentry->d_name when non-NULL. Reviewed-by: Jeff Layton Signed-off-by: Al Viro