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fanotify: limit reporting of event with non-decodeable file handles
Commita95aef69a7
("fanotify: support reporting non-decodeable file handles") merged in v6.5-rc1, added the ability to use an fanotify group with FAN_REPORT_FID mode to watch filesystems that do not support nfs export, but do know how to encode non-decodeable file handles, with the newly introduced AT_HANDLE_FID flag. At the time that this commit was merged, there were no filesystems in-tree with those traits. Commit16aac5ad1f
("ovl: support encoding non-decodable file handles"), merged in v6.6-rc1, added this trait to overlayfs, thus allowing fanotify watching of overlayfs with FAN_REPORT_FID mode. In retrospect, allowing an fanotify filesystem/mount mark on such filesystem in FAN_REPORT_FID mode will result in getting events with file handles, without the ability to resolve the filesystem objects from those file handles (i.e. no open_by_handle_at() support). For v6.6, the safer option would be to allow this mode for inode marks only, where the caller has the opportunity to use name_to_handle_at() at the time of setting the mark. In the future we can revise this decision. Fixes:a95aef69a7
("fanotify: support reporting non-decodeable file handles") Signed-off-by: Amir Goldstein <amir73il@gmail.com> Signed-off-by: Jan Kara <jack@suse.cz> Message-Id: <20231018100000.2453965-2-amir73il@gmail.com>
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dd72f9c7e5
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@ -1585,16 +1585,25 @@ static int fanotify_test_fsid(struct dentry *dentry, __kernel_fsid_t *fsid)
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}
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/* Check if filesystem can encode a unique fid */
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static int fanotify_test_fid(struct dentry *dentry)
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static int fanotify_test_fid(struct dentry *dentry, unsigned int flags)
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{
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unsigned int mark_type = flags & FANOTIFY_MARK_TYPE_BITS;
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const struct export_operations *nop = dentry->d_sb->s_export_op;
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/*
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* We need to make sure that the file system supports at least
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* encoding a file handle so user can use name_to_handle_at() to
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* compare fid returned with event to the file handle of watched
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* objects. However, even the relaxed AT_HANDLE_FID flag requires
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* at least empty export_operations for ecoding unique file ids.
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* We need to make sure that the filesystem supports encoding of
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* file handles so user can use name_to_handle_at() to compare fids
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* reported with events to the file handle of watched objects.
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*/
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if (!dentry->d_sb->s_export_op)
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if (!nop)
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return -EOPNOTSUPP;
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/*
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* For sb/mount mark, we also need to make sure that the filesystem
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* supports decoding file handles, so user has a way to map back the
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* reported fids to filesystem objects.
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*/
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if (mark_type != FAN_MARK_INODE && !nop->fh_to_dentry)
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return -EOPNOTSUPP;
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return 0;
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@ -1812,7 +1821,7 @@ static int do_fanotify_mark(int fanotify_fd, unsigned int flags, __u64 mask,
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if (ret)
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goto path_put_and_out;
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ret = fanotify_test_fid(path.dentry);
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ret = fanotify_test_fid(path.dentry, flags);
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if (ret)
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goto path_put_and_out;
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