kernel.git/fs/namei.c, branch linux-6.7.y

new helper: user_path_locked_at()

2024-02-16T18:14:30Z

commit 74d016ecc1a7974664e98d1afbf649cd4e0e0423 upstream. Equivalent of kern_path_locked() taking dfd/userland name. User introduced in the next commit. Signed-off-by: Al Viro Signed-off-by: Greg Kroah-Hartman

rename(): fix the locking of subdirectories

2024-02-01T00:21:03Z

commit 22e111ed6c83dcde3037fc81176012721bc34c0b upstream. We should never lock two subdirectories without having taken ->s_vfs_rename_mutex; inode pointer order or not, the "order" proposed in 28eceeda130f "fs: Lock moved directories" is not transitive, with the usual consequences. The rationale for locking renamed subdirectory in all cases was the possibility of race between rename modifying .. in a subdirectory to reflect the new parent and another thread modifying the same subdirectory. For a lot of filesystems that's not a problem, but for some it can lead to trouble (e.g. the case when short directory contents is kept in the inode, but creating a file in it might push it across the size limit and copy its contents into separate data block(s)). However, we need that only in case when the parent does change - otherwise ->rename() doesn't need to do anything with .. entry in the first place. Some instances are lazy and do a tautological update anyway, but it's really not hard to avoid. Amended locking rules for rename(): find the parent(s) of source and target if source and target have the same parent lock the common parent else lock ->s_vfs_rename_mutex lock both parents, in ancestor-first order; if neither is an ancestor of another, lock the parent of source first. find the source and target. if source and target have the same parent if operation is an overwriting rename of a subdirectory lock the target subdirectory else if source is a subdirectory lock the source if target is a subdirectory lock the target lock non-directories involved, in inode pointer order if both source and target are such. That way we are guaranteed that parents are locked (for obvious reasons), that any renamed non-directory is locked (nfsd relies upon that), that any victim is locked (emptiness check needs that, among other things) and subdirectory that changes parent is locked (needed to protect the update of .. entries). We are also guaranteed that any operation locking more than one directory either takes ->s_vfs_rename_mutex or locks a parent followed by its child. Cc: stable@vger.kernel.org Fixes: 28eceeda130f "fs: Lock moved directories" Reviewed-by: Jan Kara Signed-off-by: Al Viro Signed-off-by: Greg Kroah-Hartman

Merge tag 'vfs-6.7.misc' of gitolite.kernel.org:pub/scm/linux/kernel/git/vfs/vfs

2023-10-30T19:14:19Z

Pull misc vfs updates from Christian Brauner: "This contains the usual miscellaneous features, cleanups, and fixes for vfs and individual fses. Features: - Rename and export helpers that get write access to a mount. They are used in overlayfs to get write access to the upper mount. - Print the pretty name of the root device on boot failure. This helps in scenarios where we would usually only print "unknown-block(1,2)". - Add an internal SB_I_NOUMASK flag. This is another part in the endless POSIX ACL saga in a way. When POSIX ACLs are enabled via SB_POSIXACL the vfs cannot strip the umask because if the relevant inode has POSIX ACLs set it might take the umask from there. But if the inode doesn't have any POSIX ACLs set then we apply the umask in the filesytem itself. So we end up with: (1) no SB_POSIXACL -> strip umask in vfs (2) SB_POSIXACL -> strip umask in filesystem The umask semantics associated with SB_POSIXACL allowed filesystems that don't even support POSIX ACLs at all to raise SB_POSIXACL purely to avoid umask stripping. That specifically means NFS v4 and Overlayfs. NFS v4 does it because it delegates this to the server and Overlayfs because it needs to delegate umask stripping to the upper filesystem, i.e., the filesystem used as the writable layer. This went so far that SB_POSIXACL is raised eve on kernels that don't even have POSIX ACL support at all. Stop this blatant abuse and add SB_I_NOUMASK which is an internal superblock flag that filesystems can raise to opt out of umask handling. That should really only be the two mentioned above. It's not that we want any filesystems to do this. Ideally we have all umask handling always in the vfs. - Make overlayfs use SB_I_NOUMASK too. - Now that we have SB_I_NOUMASK, stop checking for SB_POSIXACL in IS_POSIXACL() if the kernel doesn't have support for it. This is a very old patch but it's only possible to do this now with the wider cleanup that was done. - Follow-up work on fake path handling from last cycle. Citing mostly from Amir: When overlayfs was first merged, overlayfs files of regular files and directories, the ones that are installed in file table, had a "fake" path, namely, f_path is the overlayfs path and f_inode is the "real" inode on the underlying filesystem. In v6.5, we took another small step by introducing of the backing_file container and the file_real_path() helper. This change allowed vfs and filesystem code to get the "real" path of an overlayfs backing file. With this change, we were able to make fsnotify work correctly and report events on the "real" filesystem objects that were accessed via overlayfs. This method works fine, but it still leaves the vfs vulnerable to new code that is not aware of files with fake path. A recent example is commit db1d1e8b9867 ("IMA: use vfs_getattr_nosec to get the i_version"). This commit uses direct referencing to f_path in IMA code that otherwise uses file_inode() and file_dentry() to reference the filesystem objects that it is measuring. This contains work to switch things around: instead of having filesystem code opt-in to get the "real" path, have generic code opt-in for the "fake" path in the few places that it is needed. Is it far more likely that new filesystems code that does not use the file_dentry() and file_real_path() helpers will end up causing crashes or averting LSM/audit rules if we keep the "fake" path exposed by default. This change already makes file_dentry() moot, but for now we did not change this helper just added a WARN_ON() in ovl_d_real() to catch if we have made any wrong assumptions. After the dust settles on this change, we can make file_dentry() a plain accessor and we can drop the inode argument to ->d_real(). - Switch struct file to SLAB_TYPESAFE_BY_RCU. This looks like a small change but it really isn't and I would like to see everyone on their tippie toes for any possible bugs from this work. Essentially we've been doing most of what SLAB_TYPESAFE_BY_RCU for files since a very long time because of the nasty interactions between the SCM_RIGHTS file descriptor garbage collection. So extending it makes a lot of sense but it is a subtle change. There are almost no places that fiddle with file rcu semantics directly and the ones that did mess around with struct file internal under rcu have been made to stop doing that because it really was always dodgy. I forgot to put in the link tag for this change and the discussion in the commit so adding it into the merge message: https://lore.kernel.org/r/20230926162228.68666-1-mjguzik@gmail.com Cleanups: - Various smaller pipe cleanups including the removal of a spin lock that was only used to protect against writes without pipe_lock() from O_NOTIFICATION_PIPE aka watch queues. As that was never implemented remove the additional locking from pipe_write(). - Annotate struct watch_filter with the new __counted_by attribute. - Clarify do_unlinkat() cleanup so that it doesn't look like an extra iput() is done that would cause issues. - Simplify file cleanup when the file has never been opened. - Use module helper instead of open-coding it. - Predict error unlikely for stale retry. - Use WRITE_ONCE() for mount expiry field instead of just commenting that one hopes the compiler doesn't get smart. Fixes: - Fix readahead on block devices. - Fix writeback when layztime is enabled and inodes whose timestamp is the only thing that changed reside on wb->b_dirty_time. This caused excessively large zombie memory cgroup when lazytime was enabled as such inodes weren't handled fast enough. - Convert BUG_ON() to WARN_ON_ONCE() in open_last_lookups()" * tag 'vfs-6.7.misc' of gitolite.kernel.org:pub/scm/linux/kernel/git/vfs/vfs: (26 commits) file, i915: fix file reference for mmap_singleton() vfs: Convert BUG_ON to WARN_ON_ONCE in open_last_lookups writeback, cgroup: switch inodes with dirty timestamps to release dying cgwbs chardev: Simplify usage of try_module_get() ovl: rely on SB_I_NOUMASK fs: fix umask on NFS with CONFIG_FS_POSIX_ACL=n fs: store real path instead of fake path in backing file f_path fs: create helper file_user_path() for user displayed mapped file path fs: get mnt_writers count for an open backing file's real path vfs: stop counting on gcc not messing with mnt_expiry_mark if not asked vfs: predict the error in retry_estale as unlikely backing file: free directly vfs: fix readahead(2) on block devices io_uring: use files_lookup_fd_locked() file: convert to SLAB_TYPESAFE_BY_RCU vfs: shave work on failed file open fs: simplify misleading code to remove ambiguity regarding ihold()/iput() watch_queue: Annotate struct watch_filter with __counted_by fs/pipe: use spinlock in pipe_read() only if there is a watch_queue fs/pipe: remove unnecessary spinlock from pipe_write() ...

vfs: Convert BUG_ON to WARN_ON_ONCE in open_last_lookups

2023-10-24T08:51:05Z

The calling code actually handles -ECHILD, so this BUG_ON can be converted to WARN_ON_ONCE. Signed-off-by: Bernd Schubert Link: https://lore.kernel.org/r/20231023184718.11143-1-bschubert@ddn.com Cc: Christian Brauner Cc: Al Viro Cc: Amir Goldstein Cc: Dharmendra Singh Cc: Miklos Szeredi Cc: linux-fsdevel@vger.kernel.org Signed-off-by: Christian Brauner

vfs: shave work on failed file open

2023-10-19T09:02:48Z

Failed opens (mostly ENOENT) legitimately happen a lot, for example here are stats from stracing kernel build for few seconds (strace -fc make): % time seconds usecs/call calls errors syscall ------ ----------- ----------- --------- --------- ------------------ 0.76 0.076233 5 15040 3688 openat (this is tons of header files tried in different paths) In the common case of there being nothing to close (only the file object to free) there is a lot of overhead which can be avoided. This is most notably delegation of freeing to task_work, which comes with an enormous cost (see 021a160abf62 ("fs: use __fput_sync in close(2)" for an example). Benchmarked with will-it-scale with a custom testcase based on tests/open1.c, stuffed into tests/openneg.c: [snip] while (1) { int fd = open("/tmp/nonexistent", O_RDONLY); assert(fd == -1); (*iterations)++; } [/snip] Sapphire Rapids, openneg_processes -t 1 (ops/s): before: 1950013 after: 2914973 (+49%) file refcount is checked as a safety belt against buggy consumers with an atomic cmpxchg. Technically it is not necessary, but it happens to not be measurable due to several other atomics which immediately follow. Optmizing them away to make this atomic into a problem is left as an exercise for the reader. v2: - unexport fput_badopen and move to fs/internal.h - handle the refcount with cmpxchg, adjust commentary accordingly - tweak the commit message Signed-off-by: Mateusz Guzik Link: https://lore.kernel.org/r/20230926162228.68666-1-mjguzik@gmail.com Signed-off-by: Christian Brauner

fs: simplify misleading code to remove ambiguity regarding ihold()/iput()

2023-10-19T09:02:48Z

Because 'inode' is being initialised before checking if 'dentry' is negative it looks like an extra iput() on 'inode' may happen since the ihold() is done only if the dentry is *not* negative. In reality this doesn't happen because d_is_negative() is never true if ->d_inode is NULL. This patch only makes the code easier to understand, as I was initially mislead by it. Signed-off-by: Luís Henriques Link: https://lore.kernel.org/r/20230928152341.303-1-lhenriques@suse.de Signed-off-by: Christian Brauner

fs: add a new SB_I_NOUMASK flag

2023-10-19T09:02:47Z

SB_POSIXACL must be set when a filesystem supports POSIX ACLs, but NFSv4 also sets this flag to prevent the VFS from applying the umask on newly-created files. NFSv4 doesn't support POSIX ACLs however, which causes confusion when other subsystems try to test for them. Add a new SB_I_NOUMASK flag that allows filesystems to opt-in to umask stripping without advertising support for POSIX ACLs. Set the new flag on NFSv4 instead of SB_POSIXACL. Also, move mode_strip_umask to namei.h and convert init_mknod and init_mkdir to use it. Signed-off-by: Jeff Layton Message-Id: <20230911-acl-fix-v3-1-b25315333f6c@kernel.org> Signed-off-by: Christian Brauner

audit,io_uring: io_uring openat triggers audit reference count underflow

2023-10-13T16:34:46Z

An io_uring openat operation can update an audit reference count from multiple threads resulting in the call trace below. A call to io_uring_submit() with a single openat op with a flag of IOSQE_ASYNC results in the following reference count updates. These first part of the system call performs two increments that do not race. do_syscall_64() __do_sys_io_uring_enter() io_submit_sqes() io_openat_prep() __io_openat_prep() getname() getname_flags() /* update 1 (increment) */ __audit_getname() /* update 2 (increment) */ The openat op is queued to an io_uring worker thread which starts the opportunity for a race. The system call exit performs one decrement. do_syscall_64() syscall_exit_to_user_mode() syscall_exit_to_user_mode_prepare() __audit_syscall_exit() audit_reset_context() putname() /* update 3 (decrement) */ The io_uring worker thread performs one increment and two decrements. These updates can race with the system call decrement. io_wqe_worker() io_worker_handle_work() io_wq_submit_work() io_issue_sqe() io_openat() io_openat2() do_filp_open() path_openat() __audit_inode() /* update 4 (increment) */ putname() /* update 5 (decrement) */ __audit_uring_exit() audit_reset_context() putname() /* update 6 (decrement) */ The fix is to change the refcnt member of struct audit_names from int to atomic_t. kernel BUG at fs/namei.c:262! Call Trace: ... ? putname+0x68/0x70 audit_reset_context.part.0.constprop.0+0xe1/0x300 __audit_uring_exit+0xda/0x1c0 io_issue_sqe+0x1f3/0x450 ? lock_timer_base+0x3b/0xd0 io_wq_submit_work+0x8d/0x2b0 ? __try_to_del_timer_sync+0x67/0xa0 io_worker_handle_work+0x17c/0x2b0 io_wqe_worker+0x10a/0x350 Cc: stable@vger.kernel.org Link: https://lore.kernel.org/lkml/MW2PR2101MB1033FFF044A258F84AEAA584F1C9A@MW2PR2101MB1033.namprd21.prod.outlook.com/ Fixes: 5bd2182d58e9 ("audit,io_uring,io-wq: add some basic audit support to io_uring") Signed-off-by: Dan Clash Link: https://lore.kernel.org/r/20231012215518.GA4048@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net Reviewed-by: Jens Axboe Signed-off-by: Christian Brauner

fs: Fix kernel-doc warnings

2023-08-19T10:12:12Z

These have a variety of causes and a corresponding variety of solutions. Signed-off-by: "Matthew Wilcox (Oracle)" Message-Id: <20230818200824.2720007-1-willy@infradead.org> Signed-off-by: Christian Brauner

fs: Fix error checking for d_hash_and_lookup()

2023-07-14T15:01:23Z

The d_hash_and_lookup() function returns error pointers or NULL. Most incorrect error checks were fixed, but the one in int path_pts() was forgotten. Fixes: eedf265aa003 ("devpts: Make each mount of devpts an independent filesystem.") Signed-off-by: Wang Ming Message-Id: <20230713120555.7025-1-machel@vivo.com> Signed-off-by: Christian Brauner