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ovl: support encoding non-decodable file handles
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When all layers support file handles, we support encoding non-decodable
file handles (a.k.a. fid) even with nfs_export=off.

When file handles do not need to be decoded, we do not need to copy up
redirected lower directories on encode, and we encode also non-indexed
upper with lower file handle, so fid will not change on copy up.

This enables reporting fanotify events with file handles on overlayfs
with default config/mount options.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
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Amir Goldstein committed Aug 12, 2023
1 parent 0c71faf commit 16aac5a
Showing 5 changed files with 32 additions and 7 deletions.
26 changes: 20 additions & 6 deletions fs/overlayfs/export.c
Original file line number Diff line number Diff line change
@@ -174,28 +174,37 @@ static int ovl_connect_layer(struct dentry *dentry)
* U = upper file handle
* L = lower file handle
*
* (*) Connecting an overlay dir from real lower dentry is not always
* (*) Decoding a connected overlay dir from real lower dentry is not always
* possible when there are redirects in lower layers and non-indexed merge dirs.
* To mitigate those case, we may copy up the lower dir ancestor before encode
* a lower dir file handle.
* of a decodable file handle for non-upper dir.
*
* Return 0 for upper file handle, > 0 for lower file handle or < 0 on error.
*/
static int ovl_check_encode_origin(struct dentry *dentry)
{
struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
bool decodable = ofs->config.nfs_export;

/* Lower file handle for non-upper non-decodable */
if (!ovl_dentry_upper(dentry) && !decodable)
return 0;

/* Upper file handle for pure upper */
if (!ovl_dentry_lower(dentry))
return 0;

/*
* Upper file handle for non-indexed upper.
*
* Root is never indexed, so if there's an upper layer, encode upper for
* root.
*/
if (ovl_dentry_upper(dentry) &&
if (dentry == dentry->d_sb->s_root)
return 0;

/*
* Upper decodable file handle for non-indexed upper.
*/
if (ovl_dentry_upper(dentry) && decodable &&
!ovl_test_flag(OVL_INDEX, d_inode(dentry)))
return 0;

@@ -205,7 +214,7 @@ static int ovl_check_encode_origin(struct dentry *dentry)
* ovl_connect_layer() will try to make origin's layer "connected" by
* copying up a "connectable" ancestor.
*/
if (d_is_dir(dentry) && ovl_upper_mnt(ofs))
if (d_is_dir(dentry) && ovl_upper_mnt(ofs) && decodable)
return ovl_connect_layer(dentry);

/* Lower file handle for indexed and non-upper dir/non-dir */
@@ -876,3 +885,8 @@ const struct export_operations ovl_export_operations = {
.get_name = ovl_get_name,
.get_parent = ovl_get_parent,
};

/* encode_fh() encodes non-decodable file handles with nfs_export=off */
const struct export_operations ovl_export_fid_operations = {
.encode_fh = ovl_encode_fh,
};
2 changes: 1 addition & 1 deletion fs/overlayfs/inode.c
Original file line number Diff line number Diff line change
@@ -1311,7 +1311,7 @@ static bool ovl_hash_bylower(struct super_block *sb, struct dentry *upper,
return false;

/* No, if non-indexed upper with NFS export */
if (sb->s_export_op && upper)
if (ofs->config.nfs_export && upper)
return false;

/* Otherwise, hash by lower inode for fsnotify */
1 change: 1 addition & 0 deletions fs/overlayfs/overlayfs.h
Original file line number Diff line number Diff line change
@@ -799,6 +799,7 @@ int ovl_set_origin(struct ovl_fs *ofs, struct dentry *lower,

/* export.c */
extern const struct export_operations ovl_export_operations;
extern const struct export_operations ovl_export_fid_operations;

/* super.c */
int ovl_fill_super(struct super_block *sb, struct fs_context *fc);
1 change: 1 addition & 0 deletions fs/overlayfs/ovl_entry.h
Original file line number Diff line number Diff line change
@@ -82,6 +82,7 @@ struct ovl_fs {
const struct cred *creator_cred;
bool tmpfile;
bool noxattr;
bool nofh;
/* Did we take the inuse lock? */
bool upperdir_locked;
bool workdir_locked;
9 changes: 9 additions & 0 deletions fs/overlayfs/super.c
Original file line number Diff line number Diff line change
@@ -400,6 +400,7 @@ static int ovl_lower_dir(const char *name, struct path *path,
pr_warn("fs on '%s' does not support file handles, falling back to index=off,nfs_export=off.\n",
name);
}
ofs->nofh |= !fh_type;
/*
* Decoding origin file handle is required for persistent st_ino.
* Without persistent st_ino, xino=auto falls back to xino=off.
@@ -818,6 +819,7 @@ static int ovl_make_workdir(struct super_block *sb, struct ovl_fs *ofs,
ofs->config.index = false;
pr_warn("upper fs does not support file handles, falling back to index=off.\n");
}
ofs->nofh |= !fh_type;

/* Check if upper fs has 32bit inode numbers */
if (fh_type != FILEID_INO32_GEN)
@@ -1452,8 +1454,15 @@ int ovl_fill_super(struct super_block *sb, struct fs_context *fc)
ofs->config.nfs_export = false;
}

/*
* Support encoding decodable file handles with nfs_export=on
* and encoding non-decodable file handles with nfs_export=off
* if all layers support file handles.
*/
if (ofs->config.nfs_export)
sb->s_export_op = &ovl_export_operations;
else if (!ofs->nofh)
sb->s_export_op = &ovl_export_fid_operations;

/* Never override disk quota limits or use reserved space */
cap_lower(cred->cap_effective, CAP_SYS_RESOURCE);

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