ucount: check for CAP_SYS_RESOURCE using ns_capable_noaudit()

The user.* sysctls implement the ctl_table_root::permissions hook and they
override the file access mode based on the CAP_SYS_RESOURCE capability (at
most rwx if capable, at most r-- if not).  The capability is being checked
unconditionally, so if an LSM denies the capability, an audit record may
be logged even when access is in fact granted.

Given the logic in the set_permissions() function in kernel/ucount.c and
the unfortunate way the permission checking is implemented, it doesn't
seem viable to avoid false positive denials by deferring the capability
check.  Thus, do the same as in net_ctl_permissions() (net/sysctl_net.c) -
switch from ns_capable() to ns_capable_noaudit(), so that the check never
logs an audit record.

Link: https://lkml.kernel.org/r/20260122140745.239428-1-omosnace@redhat.com
Fixes: dbec28460a89 ("userns: Add per user namespace sysctls.")
Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
Reviewed-by: Paul Moore <paul@paul-moore.com>
Acked-by: Serge Hallyn <serge@hallyn.com>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Alexey Gladkov <legion@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/kernel/ucount.c b/kernel/ucount.c
index 586af49fc03e42be072b2c8c6762dd66c37bc927..fc4a8f2d3096513db2667311550772491d52c185 100644 (file)
--- a/kernel/ucount.c
+++ b/kernel/ucount.c
@@ -47,7 +47,7 @@ static int set_permissions(struct ctl_table_header *head,
        int mode;
 
        /* Allow users with CAP_SYS_RESOURCE unrestrained access */
-       if (ns_capable(user_ns, CAP_SYS_RESOURCE))
+       if (ns_capable_noaudit(user_ns, CAP_SYS_RESOURCE))
                mode = (table->mode & S_IRWXU) >> 6;
        else
        /* Allow all others at most read-only access */