On Sun, May 10, 2020 at 11:15:07PM -0300, Marcos Paulo de Souza wrote: > 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. > > 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 > CC: stable@xxxxxxxxxxxxxxx > Suggested-by: Filipe Manana <fdmanana@xxxxxxxx> > Reviewed-by: Filipe Manana <fdmanana@xxxxxxxx> > Signed-off-by: Marcos Paulo de Souza <mpdesouza@xxxxxxxx> > --- > Changes from v2: > * Tag Stable correctly > * Forgot to add v2 in the latest patch. Now set to v3 to avoid confusion > > Changes from v1: > * Constify name var in send_capabilities function (suggested by Filipe) > * Changed btrfs_alloc_path -> alloc_path_for_send() in send_capabilities > (suggested by Filipe) > * Removed a redundant sentence in the commit message (suggested by Filipe) > * Added the Reviewed-By tag from Filipe > > 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..2b378e32e7dc 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 */ Comments should start with an uppercase > + 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; > + const char *name = XATTR_NAME_CAPS; > + char *buf = NULL; > + int buf_len; > + int ret = 0; > + > + path = alloc_path_for_send(); > + if (!path) > + return -ENOMEM; > + > + di = btrfs_lookup_xattr(NULL, sctx->send_root, path, sctx->cur_ino, > + name, strlen(name), 0); As Filipe pointed out in previous iteration, this could be directly XATTR_NAME_CAPS instead of the temporary variable. I'd prefer it that way too, XATTR_NAME_CAPS is a plain string and strings get merged at link time. Also compiler replaces strlen("string") with the number. > + 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)); This is probably copy&pasted, but the char* typecast is not necessary and the whole expression could be data_ptr = (unsigned long)(di + 1) + btrfs_dir_name_len(leaf, di); > + read_extent_buffer(leaf, buf, data_ptr, > + btrfs_dir_data_len(leaf, di)); btrfs_dir_data_len(leaf, di) is cached as buf_len from before so it should be used as well.
