open_by_handle_at(2) can fail with -ESTALE with a valid handle returned by a previous name_to_handle_at(2) for evicted fuse inodes, which is especially common when entry_valid_timeout is 0, e.g. when the fuse daemon is in "cache=none" mode. The time sequence is like: name_to_handle_at(2) # succeed evict fuse inode open_by_handle_at(2) # fail The root cause is that, with 0 entry_valid_timeout, the dput() called in name_to_handle_at(2) will trigger iput -> evict(), which will send FUSE_FORGET to the daemon. The following open_by_handle_at(2) will send a new FUSE_LOOKUP request upon inode cache miss since the previous inode eviction. Then the fuse daemon may fail the FUSE_LOOKUP request with -ENOENT as the cached metadata of the requested inode has already been cleaned up during the previous FUSE_FORGET. The returned -ENOENT is treated as -ESTALE when open_by_handle_at(2) returns. This confuses the application somehow, as open_by_handle_at(2) fails when the previous name_to_handle_at(2) succeeds. The returned errno is also confusing as the requested file is not deleted and already there. It is reasonable to fail name_to_handle_at(2) early in this case, after which the application can fallback to open(2) to access files. Since this issue typically appears when entry_valid_timeout is 0 which is configured by the fuse daemon, the fuse daemon is the right person to explicitly disable the export when required. Also considering FUSE_EXPORT_SUPPORT actually indicates the support for lookups of "." and "..", and there are existing fuse daemons supporting export without FUSE_EXPORT_SUPPORT set, for compatibility, we add a new INIT flag for such purpose. Signed-off-by: Jingbo Xu <jefflexu@xxxxxxxxxxxxxxxxx> --- RFC: https://lore.kernel.org/all/20240123093701.94166-1-jefflexu@xxxxxxxxxxxxxxxxx/ --- fs/fuse/inode.c | 11 ++++++++++- include/uapi/linux/fuse.h | 2 ++ 2 files changed, 12 insertions(+), 1 deletion(-) diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c index 2a6d44f91729..851940c0e930 100644 --- a/fs/fuse/inode.c +++ b/fs/fuse/inode.c @@ -1110,6 +1110,11 @@ static struct dentry *fuse_get_parent(struct dentry *child) return parent; } +/* only for fid encoding; no support for file handle */ +static const struct export_operations fuse_fid_operations = { + .encode_fh = fuse_encode_fh, +}; + static const struct export_operations fuse_export_operations = { .fh_to_dentry = fuse_fh_to_dentry, .fh_to_parent = fuse_fh_to_parent, @@ -1284,6 +1289,8 @@ static void process_init_reply(struct fuse_mount *fm, struct fuse_args *args, fc->create_supp_group = 1; if (flags & FUSE_DIRECT_IO_ALLOW_MMAP) fc->direct_io_allow_mmap = 1; + if (flags & FUSE_NO_EXPORT_SUPPORT) + fm->sb->s_export_op = &fuse_fid_operations; } else { ra_pages = fc->max_read / PAGE_SIZE; fc->no_lock = 1; @@ -1330,7 +1337,8 @@ void fuse_send_init(struct fuse_mount *fm) FUSE_NO_OPENDIR_SUPPORT | FUSE_EXPLICIT_INVAL_DATA | FUSE_HANDLE_KILLPRIV_V2 | FUSE_SETXATTR_EXT | FUSE_INIT_EXT | FUSE_SECURITY_CTX | FUSE_CREATE_SUPP_GROUP | - FUSE_HAS_EXPIRE_ONLY | FUSE_DIRECT_IO_ALLOW_MMAP; + FUSE_HAS_EXPIRE_ONLY | FUSE_DIRECT_IO_ALLOW_MMAP | + FUSE_NO_EXPORT_SUPPORT; #ifdef CONFIG_FUSE_DAX if (fm->fc->dax) flags |= FUSE_MAP_ALIGNMENT; @@ -1527,6 +1535,7 @@ static int fuse_fill_super_submount(struct super_block *sb, sb->s_bdi = bdi_get(parent_sb->s_bdi); sb->s_xattr = parent_sb->s_xattr; + sb->s_export_op = parent_sb->s_export_op; sb->s_time_gran = parent_sb->s_time_gran; sb->s_blocksize = parent_sb->s_blocksize; sb->s_blocksize_bits = parent_sb->s_blocksize_bits; diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h index e7418d15fe39..8274c0cd5d61 100644 --- a/include/uapi/linux/fuse.h +++ b/include/uapi/linux/fuse.h @@ -410,6 +410,7 @@ struct fuse_file_lock { * symlink and mknod (single group that matches parent) * FUSE_HAS_EXPIRE_ONLY: kernel supports expiry-only entry invalidation * FUSE_DIRECT_IO_ALLOW_MMAP: allow shared mmap in FOPEN_DIRECT_IO mode. + * FUSE_NO_EXPORT_SUPPORT: explicitly disable export support */ #define FUSE_ASYNC_READ (1 << 0) #define FUSE_POSIX_LOCKS (1 << 1) @@ -449,6 +450,7 @@ struct fuse_file_lock { #define FUSE_CREATE_SUPP_GROUP (1ULL << 34) #define FUSE_HAS_EXPIRE_ONLY (1ULL << 35) #define FUSE_DIRECT_IO_ALLOW_MMAP (1ULL << 36) +#define FUSE_NO_EXPORT_SUPPORT (1ULL << 37) /* Obsolete alias for FUSE_DIRECT_IO_ALLOW_MMAP */ #define FUSE_DIRECT_IO_RELAX FUSE_DIRECT_IO_ALLOW_MMAP -- 2.19.1.6.gb485710b
