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. Reviewed-by: Amir Goldstein <amir73il@xxxxxxxxx> Signed-off-by: Jingbo Xu <jefflexu@xxxxxxxxxxxxxxxxx> --- RESEND v2: - rebase to fuse/for-next and resolve the code base conflict since the passthrough feature (no logic change since original v2) - add "Reviewed-by" tag v2: https://lore.kernel.org/all/20240126072120.71867-1-jefflexu@xxxxxxxxxxxxxxxxx/ v1: https://lore.kernel.org/linux-fsdevel/20240124113042.44300-1-jefflexu@xxxxxxxxxxxxxxxxx/ RFC: https://lore.kernel.org/all/20240123093701.94166-1-jefflexu@xxxxxxxxxxxxxxxxx/ --- fs/fuse/inode.c | 11 ++++++++++- include/uapi/linux/fuse.h | 3 +++ 2 files changed, 13 insertions(+), 1 deletion(-) diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c index c26a84439934..fb9a9a9c1f1b 100644 --- a/fs/fuse/inode.c +++ b/fs/fuse/inode.c @@ -1119,6 +1119,11 @@ 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_export_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, @@ -1311,6 +1316,8 @@ static void process_init_reply(struct fuse_mount *fm, struct fuse_args *args, fc->max_stack_depth = arg->max_stack_depth; fm->sb->s_stack_depth = arg->max_stack_depth; } + if (flags & FUSE_NO_EXPORT_SUPPORT) + fm->sb->s_export_op = &fuse_export_fid_operations; } else { ra_pages = fc->max_read / PAGE_SIZE; fc->no_lock = 1; @@ -1357,7 +1364,8 @@ 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; @@ -1558,6 +1566,7 @@ 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 1162a47b6a42..a86c2cad65ad 100644 --- a/include/uapi/linux/fuse.h +++ b/include/uapi/linux/fuse.h @@ -215,6 +215,7 @@ * 7.40 * - add max_stack_depth to fuse_init_out, add FUSE_PASSTHROUGH init flag * - add backing_id to fuse_open_out, add FOPEN_PASSTHROUGH open flag + * - add FUSE_NO_EXPORT_SUPPORT init flag */ #ifndef _LINUX_FUSE_H @@ -416,6 +417,7 @@ 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) @@ -456,6 +458,7 @@ struct fuse_file_lock { #define FUSE_HAS_EXPIRE_ONLY (1ULL << 35) #define FUSE_DIRECT_IO_ALLOW_MMAP (1ULL << 36) #define FUSE_PASSTHROUGH (1ULL << 37) +#define FUSE_NO_EXPORT_SUPPORT (1ULL << 38) /* Obsolete alias for FUSE_DIRECT_IO_ALLOW_MMAP */ #define FUSE_DIRECT_IO_RELAX FUSE_DIRECT_IO_ALLOW_MMAP -- 2.19.1.6.gb485710b
