[v5,4/6] proc: allow access in init userns for map_files with CAP_CHECKPOINT_RESTORE
diff mbox series

Message ID 20200715144954.1387760-5-areber@redhat.com
State New
Headers show
Series
  • capabilities: Introduce CAP_CHECKPOINT_RESTORE
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Commit Message

Adrian Reber July 15, 2020, 2:49 p.m. UTC
Opening files in /proc/pid/map_files when the current user is
CAP_CHECKPOINT_RESTORE capable in the root namespace is useful for
checkpointing and restoring to recover files that are unreachable via
the file system such as deleted files, or memfd files.

Signed-off-by: Adrian Reber <areber@redhat.com>
Signed-off-by: Nicolas Viennot <Nicolas.Viennot@twosigma.com>
---
 fs/proc/base.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

Comments

Cyrill Gorcunov July 15, 2020, 9:17 p.m. UTC | #1
On Wed, Jul 15, 2020 at 04:49:52PM +0200, Adrian Reber wrote:
> Opening files in /proc/pid/map_files when the current user is
> CAP_CHECKPOINT_RESTORE capable in the root namespace is useful for
> checkpointing and restoring to recover files that are unreachable via
> the file system such as deleted files, or memfd files.
> 
> Signed-off-by: Adrian Reber <areber@redhat.com>
> Signed-off-by: Nicolas Viennot <Nicolas.Viennot@twosigma.com>

I still have a plan to make this code been usable without
capabilities requirements but due to lack of spare time
for deep investigation this won't happen anytime soon.
Thus the patch looks OK to me, fwiw

Reviewed-by: Cyrill Gorcunov <gorcunov@gmail.com>
Christian Brauner July 16, 2020, 8:51 a.m. UTC | #2
On Wed, Jul 15, 2020 at 04:49:52PM +0200, Adrian Reber wrote:
> Opening files in /proc/pid/map_files when the current user is
> CAP_CHECKPOINT_RESTORE capable in the root namespace is useful for
> checkpointing and restoring to recover files that are unreachable via
> the file system such as deleted files, or memfd files.
> 
> Signed-off-by: Adrian Reber <areber@redhat.com>
> Signed-off-by: Nicolas Viennot <Nicolas.Viennot@twosigma.com>
> ---
>  fs/proc/base.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index 65893686d1f1..cada783f229e 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -2194,16 +2194,16 @@ struct map_files_info {
>  };
>  
>  /*
> - * Only allow CAP_SYS_ADMIN to follow the links, due to concerns about how the
> - * symlinks may be used to bypass permissions on ancestor directories in the
> - * path to the file in question.
> + * Only allow CAP_SYS_ADMIN and CAP_CHECKPOINT_RESTORE to follow the links, due
> + * to concerns about how the symlinks may be used to bypass permissions on
> + * ancestor directories in the path to the file in question.
>   */
>  static const char *
>  proc_map_files_get_link(struct dentry *dentry,
>  			struct inode *inode,
>  		        struct delayed_call *done)
>  {
> -	if (!capable(CAP_SYS_ADMIN))
> +	if (!capable(CAP_SYS_ADMIN) || !capable(CAP_CHECKPOINT_RESTORE))

So right now, when I'd do

git grep checkpoint_restore_ns_capable

I'd not hit that codepath which isn't great. So I'd suggest to use:

if (!checkpoint_restore_ns_capable(&init_user_ns))

at the end of the day, capable(<cap>) just calls
ns_capable(&init_user_ns, <cap>) anyway.

Thanks!
Christian

Patch
diff mbox series

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 65893686d1f1..cada783f229e 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2194,16 +2194,16 @@  struct map_files_info {
 };
 
 /*
- * Only allow CAP_SYS_ADMIN to follow the links, due to concerns about how the
- * symlinks may be used to bypass permissions on ancestor directories in the
- * path to the file in question.
+ * Only allow CAP_SYS_ADMIN and CAP_CHECKPOINT_RESTORE to follow the links, due
+ * to concerns about how the symlinks may be used to bypass permissions on
+ * ancestor directories in the path to the file in question.
  */
 static const char *
 proc_map_files_get_link(struct dentry *dentry,
 			struct inode *inode,
 		        struct delayed_call *done)
 {
-	if (!capable(CAP_SYS_ADMIN))
+	if (!capable(CAP_SYS_ADMIN) || !capable(CAP_CHECKPOINT_RESTORE))
 		return ERR_PTR(-EPERM);
 
 	return proc_pid_get_link(dentry, inode, done);