From: Miklos Szeredi mszeredi@redhat.com
commit 9b91b6b019fda817eb52f728eb9c79b3579760bc upstream.
There's possibility of an ABBA deadlock in case of a splice write to an overlayfs file and a concurrent splice write to a corresponding real file.
The call chain for splice to an overlay file:
-> do_splice [takes sb_writers on overlay file] -> do_splice_from -> iter_file_splice_write [takes pipe->mutex] -> vfs_iter_write ... -> ovl_write_iter [takes sb_writers on real file]
And the call chain for splice to a real file:
-> do_splice [takes sb_writers on real file] -> do_splice_from -> iter_file_splice_write [takes pipe->mutex]
Syzbot successfully bisected this to commit 82a763e61e2b ("ovl: simplify file splice").
Fix by reverting the write part of the above commit and by adding missing bits from ovl_write_iter() into ovl_splice_write().
Fixes: 82a763e61e2b ("ovl: simplify file splice") Reported-and-tested-by: syzbot+579885d1a9a833336209@syzkaller.appspotmail.com Signed-off-by: Miklos Szeredi mszeredi@redhat.com Cc: Stan Hu stanhu@gmail.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/overlayfs/file.c | 47 ++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 46 insertions(+), 1 deletion(-)
--- a/fs/overlayfs/file.c +++ b/fs/overlayfs/file.c @@ -422,6 +422,51 @@ out_unlock: return ret; }
+/* + * Calling iter_file_splice_write() directly from overlay's f_op may deadlock + * due to lock order inversion between pipe->mutex in iter_file_splice_write() + * and file_start_write(real.file) in ovl_write_iter(). + * + * So do everything ovl_write_iter() does and call iter_file_splice_write() on + * the real file. + */ +static ssize_t ovl_splice_write(struct pipe_inode_info *pipe, struct file *out, + loff_t *ppos, size_t len, unsigned int flags) +{ + struct fd real; + const struct cred *old_cred; + struct inode *inode = file_inode(out); + struct inode *realinode = ovl_inode_real(inode); + ssize_t ret; + + inode_lock(inode); + /* Update mode */ + ovl_copyattr(realinode, inode); + ret = file_remove_privs(out); + if (ret) + goto out_unlock; + + ret = ovl_real_fdget(out, &real); + if (ret) + goto out_unlock; + + old_cred = ovl_override_creds(inode->i_sb); + file_start_write(real.file); + + ret = iter_file_splice_write(pipe, real.file, ppos, len, flags); + + file_end_write(real.file); + /* Update size */ + ovl_copyattr(realinode, inode); + revert_creds(old_cred); + fdput(real); + +out_unlock: + inode_unlock(inode); + + return ret; +} + static int ovl_fsync(struct file *file, loff_t start, loff_t end, int datasync) { struct fd real; @@ -731,7 +776,7 @@ const struct file_operations ovl_file_op .compat_ioctl = ovl_compat_ioctl, #endif .splice_read = generic_file_splice_read, - .splice_write = iter_file_splice_write, + .splice_write = ovl_splice_write,
.copy_file_range = ovl_copy_file_range, .remap_file_range = ovl_remap_file_range,