kernel/linux.git/fs/fuse/dir.c, branch linux-6.0.y

fuse: Add module param for CAP_SYS_ADMIN access bypassing allow_other

2022-07-21T14:06:19+00:00

Since commit 73f03c2b4b52 ("fuse: Restrict allow_other to the superblock's namespace or a descendant"), access to allow_other FUSE filesystems has been limited to users in the mounting user namespace or descendants. This prevents a process that is privileged in its userns - but not its parent namespaces - from mounting a FUSE fs w/ allow_other that is accessible to processes in parent namespaces. While this restriction makes sense overall it breaks a legitimate usecase: I have a tracing daemon which needs to peek into process' open files in order to symbolicate - similar to 'perf'. The daemon is a privileged process in the root userns, but is unable to peek into FUSE filesystems mounted by processes in child namespaces. This patch adds a module param, allow_sys_admin_access, to act as an escape hatch for this descendant userns logic and for the allow_other mount option in general. Setting allow_sys_admin_access allows processes with CAP_SYS_ADMIN in the initial userns to access FUSE filesystems irrespective of the mounting userns or whether allow_other was set. A sysadmin setting this param must trust FUSEs on the host to not DoS processes as described in 73f03c2b4b52. Signed-off-by: Dave Marchevsky Reviewed-by: Christian Brauner (Microsoft) Signed-off-by: Miklos Szeredi

fuse: fix deadlock between atomic O_TRUNC and page invalidation

2022-07-21T14:02:45+00:00

fuse_finish_open() will be called with FUSE_NOWRITE set in case of atomic O_TRUNC open(), so commit 76224355db75 ("fuse: truncate pagecache on atomic_o_trunc") replaced invalidate_inode_pages2() by truncate_pagecache() in such a case to avoid the A-A deadlock. However, we found another A-B-B-A deadlock related to the case above, which will cause the xfstests generic/464 testcase hung in our virtio-fs test environment. For example, consider two processes concurrently open one same file, one with O_TRUNC and another without O_TRUNC. The deadlock case is described below, if open(O_TRUNC) is already set_nowrite(acquired A), and is trying to lock a page (acquiring B), open() could have held the page lock (acquired B), and waiting on the page writeback (acquiring A). This would lead to deadlocks. open(O_TRUNC) ---------------------------------------------------------------- fuse_open_common inode_lock [C acquire] fuse_set_nowrite [A acquire] fuse_finish_open truncate_pagecache lock_page [B acquire] truncate_inode_page unlock_page [B release] fuse_release_nowrite [A release] inode_unlock [C release] ---------------------------------------------------------------- open() ---------------------------------------------------------------- fuse_open_common fuse_finish_open invalidate_inode_pages2 lock_page [B acquire] fuse_launder_page fuse_wait_on_page_writeback [A acquire & release] unlock_page [B release] ---------------------------------------------------------------- Besides this case, all calls of invalidate_inode_pages2() and invalidate_inode_pages2_range() in fuse code also can deadlock with open(O_TRUNC). Fix by moving the truncate_pagecache() call outside the nowrite protected region. The nowrite protection is only for delayed writeback (writeback_cache) case, where inode lock does not protect against truncation racing with writes on the server. Write syscalls racing with page cache truncation still get the inode lock protection. This patch also changes the order of filemap_invalidate_lock() vs. fuse_set_nowrite() in fuse_open_common(). This new order matches the order found in fuse_file_fallocate() and fuse_do_setattr(). Reported-by: Jiachen Zhang Tested-by: Jiachen Zhang Fixes: e4648309b85a ("fuse: truncate pending writes on O_TRUNC") Cc: Signed-off-by: Miklos Szeredi

fuse: Convert fuse to read_folio

2022-05-09T20:21:45+00:00

This is a "weak" conversion which converts straight back to using pages. A full conversion should be performed at some point, hopefully by someone familiar with the filesystem. Signed-off-by: Matthew Wilcox (Oracle)

fuse: Convert from launder_page to launder_folio

2022-03-15T12:23:30+00:00

Straightforward conversion although the helper functions still assume a single page. Signed-off-by: Matthew Wilcox (Oracle) Tested-by: Damien Le Moal Acked-by: Damien Le Moal Tested-by: Mike Marshall # orangefs Tested-by: David Howells # afs

fuse: send security context of inode on file

2021-11-25T13:05:18+00:00

When a new inode is created, send its security context to server along with creation request (FUSE_CREAT, FUSE_MKNOD, FUSE_MKDIR and FUSE_SYMLINK). This gives server an opportunity to create new file and set security context (possibly atomically). In all the configurations it might not be possible to set context atomically. Like nfs and ceph, use security_dentry_init_security() to dermine security context of inode and send it with create, mkdir, mknod, and symlink requests. Following is the information sent to server. fuse_sectx_header, fuse_secctx, xattr_name, security_context - struct fuse_secctx_header This contains total number of security contexts being sent and total size of all the security contexts (including size of fuse_secctx_header). - struct fuse_secctx This contains size of security context which follows this structure. There is one fuse_secctx instance per security context. - xattr name string This string represents name of xattr which should be used while setting security context. - security context This is the actual security context whose size is specified in fuse_secctx struct. Also add the FUSE_SECURITY_CTX flag for the `flags` field of the fuse_init_out struct. When this flag is set the kernel will append the security context for a newly created inode to the request (create, mkdir, mknod, and symlink). The server is responsible for ensuring that the inode appears atomically (preferrably) with the requested security context. For example, If the server is using SELinux and backed by a "real" linux file system that supports extended attributes it can write the security context value to /proc/thread-self/attr/fscreate before making the syscall to create the inode. This patch is based on patch from Chirantan Ekbote Signed-off-by: Vivek Goyal Signed-off-by: Miklos Szeredi

fuse: only update necessary attributes

2021-10-28T07:45:33+00:00

fuse_update_attributes() refreshes metadata for internal use. Each use needs a particular set of attributes to be refreshed, but currently that cannot be expressed and all but atime are refreshed. Add a mask argument, which lets fuse_update_get_attr() to decide based on the cache_mask and the inval_mask whether a GETATTR call is needed or not. Reported-by: Yongji Xie Signed-off-by: Miklos Szeredi

fuse: take cache_mask into account in getattr

2021-10-28T07:45:33+00:00

When deciding to send a GETATTR request take into account the cache mask (which attributes are always valid). The cache mask takes precedence over the invalid mask. This results in the GETATTR request not being sent unnecessarily. Signed-off-by: Miklos Szeredi

fuse: add cache_mask

2021-10-28T07:45:33+00:00

If writeback_cache is enabled, then the size, mtime and ctime attributes of regular files are always valid in the kernel's cache. They are retrieved from userspace only when the inode is freshly looked up. Add a more generic "cache_mask", that indicates which attributes are currently valid in cache. This patch doesn't change behavior. Signed-off-by: Miklos Szeredi

fuse: move reverting attributes to fuse_change_attributes()

2021-10-28T07:45:32+00:00

In case of writeback_cache fuse_fillattr() would revert the queried attributes to the cached version. Move this to fuse_change_attributes() in order to manage the writeback logic in a central helper. This will be necessary for patches that follow. Only fuse_do_getattr() -> fuse_fillattr() uses the attributes after calling fuse_change_attributes(), so this should not change behavior. Signed-off-by: Miklos Szeredi

fuse: simplify local variables holding writeback cache state

2021-10-28T07:45:32+00:00

There are two instances of "bool is_wb = fc->writeback_cache" where the actual use mostly involves checking "is_wb && S_ISREG(inode->i_mode)". Clean up these cases by storing the second condition in the local variable. Signed-off-by: Miklos Szeredi