kernel/linux.git/fs/fsopen.c, branch v6.12.80

fscontext: do not consume log entries when returning -EMSGSIZE

2025-10-19T14:33:33+00:00

commit 72d271a7baa7062cb27e774ac37c5459c6d20e22 upstream. Userspace generally expects APIs that return -EMSGSIZE to allow for them to adjust their buffer size and retry the operation. However, the fscontext log would previously clear the message even in the -EMSGSIZE case. Given that it is very cheap for us to check whether the buffer is too small before we remove the message from the ring buffer, let's just do that instead. While we're at it, refactor some fscontext_read() into a separate helper to make the ring buffer logic a bit easier to read. Fixes: 007ec26cdc9f ("vfs: Implement logging through fs_context") Cc: David Howells Cc: stable@vger.kernel.org # v5.2+ Signed-off-by: Aleksa Sarai Link: https://lore.kernel.org/20250807-fscontext-log-cleanups-v3-1-8d91d6242dc3@cyphar.com Signed-off-by: Christian Brauner Signed-off-by: Greg Kroah-Hartman

[tree-wide] finally take no_llseek out

2024-09-27T15:18:43+00:00

no_llseek had been defined to NULL two years ago, in commit 868941b14441 ("fs: remove no_llseek") To quote that commit, At -rc1 we'll need do a mechanical removal of no_llseek - git grep -l -w no_llseek | grep -v porting.rst | while read i; do sed -i '/\/d' $i done would do it. Unfortunately, that hadn't been done. Linus, could you do that now, so that we could finally put that thing to rest? All instances are of the form .llseek = no_llseek, so it's obviously safe. Signed-off-by: Al Viro Signed-off-by: Linus Torvalds

introduce fd_file(), convert all accessors to it.

2024-08-13T02:00:43+00:00

For any changes of struct fd representation we need to turn existing accesses to fields into calls of wrappers. Accesses to struct fd::flags are very few (3 in linux/file.h, 1 in net/socket.c, 3 in fs/overlayfs/file.c and 3 more in explicit initializers). Those can be dealt with in the commit converting to new layout; accesses to struct fd::file are too many for that. This commit converts (almost) all of f.file to fd_file(f). It's not entirely mechanical ('file' is used as a member name more than just in struct fd) and it does not even attempt to distinguish the uses in pointer context from those in boolean context; the latter will be eventually turned into a separate helper (fd_empty()). NOTE: mass conversion to fd_empty(), tempting as it might be, is a bad idea; better do that piecewise in commit that convert from fdget...() to CLASS(...). [conflicts in fs/fhandle.c, kernel/bpf/syscall.c, mm/memcontrol.c caught by git; fs/stat.c one got caught by git grep] [fs/xattr.c conflict] Reviewed-by: Christian Brauner Signed-off-by: Al Viro

vfs: retire user_path_at_empty and drop empty arg from getname_flags

2024-06-05T15:03:57+00:00

No users after do_readlinkat started doing the job on its own. Signed-off-by: Mateusz Guzik Link: https://lore.kernel.org/r/20240604155257.109500-3-mjguzik@gmail.com Reviewed-by: Jan Kara Signed-off-by: Christian Brauner

fs: fsconfig: intercept non-new mount API in advance for FSCONFIG_CMD_CREATE_EXCL command

2024-05-27T13:58:46+00:00

fsconfig with FSCONFIG_CMD_CREATE_EXCL command requires the new mount api, here we should return -EOPNOTSUPP in advance to avoid extra procedure. Signed-off-by: Hongbo Li Link: https://lore.kernel.org/r/20240522030422.315892-1-lihongbo22@huawei.com Reviewed-by: Jan Kara Signed-off-by: Christian Brauner

fsconfig: ensure that dirfd is set to aux

2023-09-22T12:09:06+00:00

The code in fs_param_is_fd() expects param->dirfd to be set to the fd that was used to set param->file to initialize result->uint_32. So make sure it's set so users like autofs using FSCONFIG_SET_FD with the new mount api can rely on this to be set to the correct value. Link: https://lore.kernel.org/lkml/20230922-vorbringen-spaghetti-946729122076@brauner Signed-off-by: Christian Brauner

fs: add FSCONFIG_CMD_CREATE_EXCL

2023-08-14T16:48:02+00:00

Summary ======= This introduces FSCONFIG_CMD_CREATE_EXCL which will allows userspace to implement something like mount -t ext4 --exclusive /dev/sda /B which fails if a superblock for the requested filesystem does already exist: Before this patch ----------------- $ sudo ./move-mount -f xfs -o source=/dev/sda4 /A Requesting filesystem type xfs Mount options requested: source=/dev/sda4 Attaching mount at /A Moving single attached mount Setting key(source) with val(/dev/sda4) $ sudo ./move-mount -f xfs -o source=/dev/sda4 /B Requesting filesystem type xfs Mount options requested: source=/dev/sda4 Attaching mount at /B Moving single attached mount Setting key(source) with val(/dev/sda4) After this patch with --exclusive as a switch for FSCONFIG_CMD_CREATE_EXCL -------------------------------------------------------------------------- $ sudo ./move-mount -f xfs --exclusive -o source=/dev/sda4 /A Requesting filesystem type xfs Request exclusive superblock creation Mount options requested: source=/dev/sda4 Attaching mount at /A Moving single attached mount Setting key(source) with val(/dev/sda4) $ sudo ./move-mount -f xfs --exclusive -o source=/dev/sda4 /B Requesting filesystem type xfs Request exclusive superblock creation Mount options requested: source=/dev/sda4 Attaching mount at /B Moving single attached mount Setting key(source) with val(/dev/sda4) Device or resource busy | move-mount.c: 300: do_fsconfig: i xfs: reusing existing filesystem not allowed Details ======= As mentioned on the list (cf. [1]-[3]) mount requests like mount -t ext4 /dev/sda /A are ambigous for userspace. Either a new superblock has been created and mounted or an existing superblock has been reused and a bind-mount has been created. This becomes clear in the following example where two processes create the same mount for the same block device: P1 P2 fd_fs = fsopen("ext4"); fd_fs = fsopen("ext4"); fsconfig(fd_fs, FSCONFIG_SET_STRING, "source", "/dev/sda"); fsconfig(fd_fs, FSCONFIG_SET_STRING, "source", "/dev/sda"); fsconfig(fd_fs, FSCONFIG_SET_STRING, "dax", "always"); fsconfig(fd_fs, FSCONFIG_SET_STRING, "resuid", "1000"); // wins and creates superblock fsconfig(fd_fs, FSCONFIG_CMD_CREATE, ...) // finds compatible superblock of P1 // spins until P1 sets SB_BORN and grabs a reference fsconfig(fd_fs, FSCONFIG_CMD_CREATE, ...) fd_mnt1 = fsmount(fd_fs); fd_mnt2 = fsmount(fd_fs); move_mount(fd_mnt1, "/A") move_mount(fd_mnt2, "/B") Not just does P2 get a bind-mount but the mount options that P2 requestes are silently ignored. The VFS itself doesn't, can't and shouldn't enforce filesystem specific mount option compatibility. It only enforces incompatibility for read-only <-> read-write transitions: mount -t ext4 /dev/sda /A mount -t ext4 -o ro /dev/sda /B The read-only request will fail with EBUSY as the VFS can't just silently transition a superblock from read-write to read-only or vica versa without risking security issues. To userspace this silent superblock reuse can become a security issue in because there is currently no straightforward way for userspace to know that they did indeed manage to create a new superblock and didn't just reuse an existing one. This adds a new FSCONFIG_CMD_CREATE_EXCL command to fsconfig() that returns EBUSY if an existing superblock would be reused. Userspace that needs to be sure that it did create a new superblock with the requested mount options can request superblock creation using this command. If the command succeeds they can be sure that they did create a new superblock with the requested mount options. This requires the new mount api. With the old mount api it would be necessary to plumb this through every legacy filesystem's file_system_type->mount() method. If they want this feature they are most welcome to switch to the new mount api. Following is an analysis of the effect of FSCONFIG_CMD_CREATE_EXCL on each high-level superblock creation helper: (1) get_tree_nodev() Always allocate new superblock. Hence, FSCONFIG_CMD_CREATE and FSCONFIG_CMD_CREATE_EXCL are equivalent. The binderfs or overlayfs filesystems are examples. (4) get_tree_keyed() Finds an existing superblock based on sb->s_fs_info. Hence, FSCONFIG_CMD_CREATE would reuse an existing superblock whereas FSCONFIG_CMD_CREATE_EXCL would reject it with EBUSY. The mqueue or nfsd filesystems are examples. (2) get_tree_bdev() This effectively works like get_tree_keyed(). The ext4 or xfs filesystems are examples. (3) get_tree_single() Only one superblock of this filesystem type can ever exist. Hence, FSCONFIG_CMD_CREATE would reuse an existing superblock whereas FSCONFIG_CMD_CREATE_EXCL would reject it with EBUSY. The securityfs or configfs filesystems are examples. Note that some single-instance filesystems never destroy the superblock once it has been created during the first mount. For example, if securityfs has been mounted at least onces then the created superblock will never be destroyed again as long as there is still an LSM making use it. Consequently, even if securityfs is unmounted and the superblock seemingly destroyed it really isn't which means that FSCONFIG_CMD_CREATE_EXCL will continue rejecting reusing an existing superblock. This is acceptable thugh since special purpose filesystems such as this shouldn't have a need to use FSCONFIG_CMD_CREATE_EXCL anyway and if they do it's probably to make sure that mount options aren't ignored. Following is an analysis of the effect of FSCONFIG_CMD_CREATE_EXCL on filesystems that make use of the low-level sget_fc() helper directly. They're all effectively variants on get_tree_keyed(), get_tree_bdev(), or get_tree_nodev(): (5) mtd_get_sb() Similar logic to get_tree_keyed(). (6) afs_get_tree() Similar logic to get_tree_keyed(). (7) ceph_get_tree() Similar logic to get_tree_keyed(). Already explicitly allows forcing the allocation of a new superblock via CEPH_OPT_NOSHARE. This turns it into get_tree_nodev(). (8) fuse_get_tree_submount() Similar logic to get_tree_nodev(). (9) fuse_get_tree() Forces reuse of existing FUSE superblock. Forces reuse of existing superblock if passed in file refers to an existing FUSE connection. If FSCONFIG_CMD_CREATE_EXCL is specified together with an fd referring to an existing FUSE connections this would cause the superblock reusal to fail. If reusing is the intent then FSCONFIG_CMD_CREATE_EXCL shouldn't be specified. (10) fuse_get_tree() -> get_tree_nodev() Same logic as in get_tree_nodev(). (11) fuse_get_tree() -> get_tree_bdev() Same logic as in get_tree_bdev(). (12) virtio_fs_get_tree() Same logic as get_tree_keyed(). (13) gfs2_meta_get_tree() Forces reuse of existing gfs2 superblock. Mounting gfs2meta enforces that a gf2s superblock must already exist. If not, it will error out. Consequently, mounting gfs2meta with FSCONFIG_CMD_CREATE_EXCL would always fail. If reusing is the intent then FSCONFIG_CMD_CREATE_EXCL shouldn't be specified. (14) kernfs_get_tree() Similar logic to get_tree_keyed(). (15) nfs_get_tree_common() Similar logic to get_tree_keyed(). Already explicitly allows forcing the allocation of a new superblock via NFS_MOUNT_UNSHARED. This effectively turns it into get_tree_nodev(). Link: [1] https://lore.kernel.org/linux-block/20230704-fasching-wertarbeit-7c6ffb01c83d@brauner Link: [2] https://lore.kernel.org/linux-block/20230705-pumpwerk-vielversprechend-a4b1fd947b65@brauner Link: [3] https://lore.kernel.org/linux-fsdevel/20230725-einnahmen-warnschilder-17779aec0a97@brauner Reviewed-by: Josef Bacik Reviewed-by: Christoph Hellwig Reviewed-by: Jan Kara Reviewed-by: Aleksa Sarai Message-Id: <20230802-vfs-super-exclusive-v2-4-95dc4e41b870@kernel.org> Signed-off-by: Christian Brauner

fs: add vfs_cmd_reconfigure()

2023-08-14T16:48:02+00:00

Split the steps to reconfigure a superblock into a tiny helper instead of open-coding it in the switch. Reviewed-by: Christoph Hellwig Reviewed-by: Jan Kara Reviewed-by: Aleksa Sarai Message-Id: <20230802-vfs-super-exclusive-v2-3-95dc4e41b870@kernel.org> Signed-off-by: Christian Brauner

fs: add vfs_cmd_create()

2023-08-14T16:48:02+00:00

Split the steps to create a superblock into a tiny helper. This will make the next patch easier to follow. Reviewed-by: Josef Bacik Reviewed-by: Christoph Hellwig Reviewed-by: Jan Kara Reviewed-by: Aleksa Sarai Message-Id: <20230802-vfs-super-exclusive-v2-2-95dc4e41b870@kernel.org> Signed-off-by: Christian Brauner

uninline may_mount() and don't opencode it in fspick(2)/fsopen(2)

2022-05-20T03:25:10+00:00

It's done once per (mount-related) syscall and there's no point whatsoever making it inline. Signed-off-by: Al Viro