From: Marcos Paulo de Souza <mpdesouza@xxxxxxxx> [PROBLEM] Whenever a chown is executed, all capabilities of the file being touched are lost. When doing incremental send with a file with capabilities, there is a situation where the capability can be lost in the receiving side. The sequence of actions bellow shows the problem: $ mount /dev/sda fs1 $ mount /dev/sdb fs2 $ touch fs1/foo.bar $ setcap cap_sys_nice+ep fs1/foo.bar $ btrfs subvol snap -r fs1 fs1/snap_init $ btrfs send fs1/snap_init | btrfs receive fs2 $ chgrp adm fs1/foo.bar $ setcap cap_sys_nice+ep fs1/foo.bar $ btrfs subvol snap -r fs1 fs1/snap_complete $ btrfs subvol snap -r fs1 fs1/snap_incremental $ btrfs send fs1/snap_complete | btrfs receive fs2 $ btrfs send -p fs1/snap_init fs1/snap_incremental | btrfs receive fs2 At this point, only a chown was emitted by "btrfs send" since only the group was changed. This makes the cap_sys_nice capability to be dropped from fs2/snap_incremental/foo.bar [FIX] Only emit capabilities after chown is emitted. The current code first checks for xattrs that are new/changed, emits them, and later emit the chown. Now, __process_new_xattr skips capabilities, letting only finish_inode_if_needed to emit them, if they exist, for the inode being processed. Also, this patch also fixes a longstanding problem that was issuing an xattr _before_ chown. This behavior was being worked around in "btrfs receive" side by caching the capability and only applying it after chown. Now, xattrs are only emmited _after_ chown, making that hack not needed anymore. Link: https://github.com/kdave/btrfs-progs/issues/202 Suggested-by: Filipe Manana <fdmanana@xxxxxxxx> Signed-off-by: Marcos Paulo de Souza <mpdesouza@xxxxxxxx> --- The first version of the patch was an RFC Changes from RFC: * Explained about chown + drop capabilities problem in the commit message (suggested by Filipe and David) * Changed the commit message to show describe the fix (suggested by Filipe) * Skip the xattr in __process_new_xattr if it's a capability, since it'll be handled in finish_inode_if_needed now (suggested by Filipe). * Created function send_capabilities to query if the inode has caps, and if yes, emit them. * Call send_capabilities in finish_inode_if_needed _after_ the needs_chown check. (suggested by Filipe) fs/btrfs/send.c | 69 +++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 69 insertions(+) diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c index 6b86841315be..4f19965bdd82 100644 --- a/fs/btrfs/send.c +++ b/fs/btrfs/send.c @@ -23,6 +23,7 @@ #include "btrfs_inode.h" #include "transaction.h" #include "compression.h" +#include "xattr.h" /* * Maximum number of references an extent can have in order for us to attempt to @@ -4545,6 +4546,10 @@ static int __process_new_xattr(int num, struct btrfs_key *di_key, struct fs_path *p; struct posix_acl_xattr_header dummy_acl; + /* capabilities are emitted by finish_inode_if_needed */ + if (!strncmp(name, XATTR_NAME_CAPS, name_len)) + return 0; + p = fs_path_alloc(); if (!p) return -ENOMEM; @@ -5107,6 +5112,66 @@ static int send_extent_data(struct send_ctx *sctx, return 0; } +/* + * Search for a capability xattr related to sctx->cur_ino. If the capability if + * found, call send_set_xattr function to emit it. + * + * Return %0 if there isn't a capability, or when the capability was emitted + * successfully, or < %0 if an error occurred. + */ +static int send_capabilities(struct send_ctx *sctx) +{ + struct fs_path *fspath = NULL; + struct btrfs_path *path; + struct btrfs_dir_item *di; + struct extent_buffer *leaf; + unsigned long data_ptr; + char *name = XATTR_NAME_CAPS; + char *buf = NULL; + int buf_len; + int ret = 0; + + path = btrfs_alloc_path(); + if (!path) + return -ENOMEM; + + di = btrfs_lookup_xattr(NULL, sctx->send_root, path, sctx->cur_ino, + name, strlen(name), 0); + if (!di) { + /* there is no xattr for this inode */ + goto out; + } else if (IS_ERR(di)) { + ret = PTR_ERR(di); + goto out; + } + + leaf = path->nodes[0]; + buf_len = btrfs_dir_data_len(leaf, di); + + fspath = fs_path_alloc(); + buf = kmalloc(buf_len, GFP_KERNEL); + if (!fspath || !buf) { + ret = -ENOMEM; + goto out; + } + + ret = get_cur_path(sctx, sctx->cur_ino, sctx->cur_inode_gen, fspath); + if (ret < 0) + goto out; + + data_ptr = (unsigned long)((char *)(di + 1) + + btrfs_dir_name_len(leaf, di)); + read_extent_buffer(leaf, buf, data_ptr, + btrfs_dir_data_len(leaf, di)); + + ret = send_set_xattr(sctx, fspath, name, strlen(name), buf, buf_len); +out: + kfree(buf); + fs_path_free(fspath); + btrfs_free_path(path); + return ret; +} + static int clone_range(struct send_ctx *sctx, struct clone_root *clone_root, const u64 disk_byte, @@ -6010,6 +6075,10 @@ static int finish_inode_if_needed(struct send_ctx *sctx, int at_end) goto out; } + ret = send_capabilities(sctx); + if (ret < 0) + goto out; + /* * If other directory inodes depended on our current directory * inode's move/rename, now do their move/rename operations. -- 2.25.1
