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 <[email protected]>
Signed-off-by: Jingbo Xu <[email protected]>
---
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/[email protected]/
v1: https://lore.kernel.org/linux-fsdevel/[email protected]/
RFC: https://lore.kernel.org/all/[email protected]/
---
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
On Mon, 26 Feb 2024 at 04:54, Jingbo Xu <[email protected]> wrote:
>
> 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 <[email protected]>
> Signed-off-by: Jingbo Xu <[email protected]>
Applied, thanks.
Miklos