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| author | Dave Marchevsky <davemarchevsky@fb.com> | 2022-07-11 10:48:08 -0700 |
|---|---|---|
| committer | Miklos Szeredi <mszeredi@redhat.com> | 2022-07-21 16:06:19 +0200 |
| commit | 9ccf47b26b73ecf5b7278a4cb8d487d8ebb4c095 (patch) | |
| tree | a74a0364b8eb36b4824856ea84270a7a2967efd1 /fs/fuse | |
| parent | c64797809a64c73497082aa05e401a062ec1af34 (diff) | |
| download | linux-9ccf47b26b73ecf5b7278a4cb8d487d8ebb4c095.tar.bz2 | |
fuse: Add module param for CAP_SYS_ADMIN access bypassing allow_other
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 <davemarchevsky@fb.com>
Reviewed-by: Christian Brauner (Microsoft) <brauner@kernel.org>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Diffstat (limited to 'fs/fuse')
| -rw-r--r-- | fs/fuse/dir.c | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c index a93d675a726a..b585b04e815e 100644 --- a/fs/fuse/dir.c +++ b/fs/fuse/dir.c @@ -11,6 +11,7 @@ #include <linux/pagemap.h> #include <linux/file.h> #include <linux/fs_context.h> +#include <linux/moduleparam.h> #include <linux/sched.h> #include <linux/namei.h> #include <linux/slab.h> @@ -21,6 +22,11 @@ #include <linux/types.h> #include <linux/kernel.h> +static bool __read_mostly allow_sys_admin_access; +module_param(allow_sys_admin_access, bool, 0644); +MODULE_PARM_DESC(allow_sys_admin_access, + "Allow users with CAP_SYS_ADMIN in initial userns to bypass allow_other access check"); + static void fuse_advise_use_readdirplus(struct inode *dir) { struct fuse_inode *fi = get_fuse_inode(dir); @@ -1229,6 +1235,9 @@ int fuse_allow_current_process(struct fuse_conn *fc) { const struct cred *cred; + if (allow_sys_admin_access && capable(CAP_SYS_ADMIN)) + return 1; + if (fc->allow_other) return current_in_userns(fc->user_ns); |