[PATCH v6 4/7] proc: allow access in init userns for map_files with CAP_CHECKPOINT_RESTORE

[Adrian Reber]

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@xxxxxxxxxx>
Signed-off-by: Nicolas Viennot <Nicolas.Viennot@xxxxxxxxxxxx>
Reviewed-by: Cyrill Gorcunov <gorcunov@xxxxxxxxx>
---
 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..b824a8c89011 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 (!checkpoint_restore_ns_capable(&init_user_ns))
 		return ERR_PTR(-EPERM);
 
 	return proc_pid_get_link(dentry, inode, done);
-- 
2.26.2