attr: add in_group_or_capable()
commit 11c2a8700cdcabf9b639b7204a1e38e2a0b6798e upstream.
[backport to 5.15.y, prior to vfsgid_t]
In setattr_{copy,prepare}() we need to perform the same permission
checks to determine whether we need to drop the setgid bit or not.
Instead of open-coding it twice add a simple helper the encapsulates the
logic. We will reuse this helpers to make dropping the setgid bit during
write operations more consistent in a follow up patch.
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Tested-by: Leah Rumancik <leah.rumancik@gmail.com>
Acked-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
diff --git a/fs/inode.c b/fs/inode.c
index 957b2d1..a71fb82 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -2322,6 +2322,28 @@ struct timespec64 current_time(struct inode *inode)
EXPORT_SYMBOL(current_time);
/**
+ * in_group_or_capable - check whether caller is CAP_FSETID privileged
+ * @mnt_userns: user namespace of the mount @inode was found from
+ * @inode: inode to check
+ * @gid: the new/current gid of @inode
+ *
+ * Check wether @gid is in the caller's group list or if the caller is
+ * privileged with CAP_FSETID over @inode. This can be used to determine
+ * whether the setgid bit can be kept or must be dropped.
+ *
+ * Return: true if the caller is sufficiently privileged, false if not.
+ */
+bool in_group_or_capable(struct user_namespace *mnt_userns,
+ const struct inode *inode, kgid_t gid)
+{
+ if (in_group_p(gid))
+ return true;
+ if (capable_wrt_inode_uidgid(mnt_userns, inode, CAP_FSETID))
+ return true;
+ return false;
+}
+
+/**
* mode_strip_sgid - handle the sgid bit for non-directories
* @mnt_userns: User namespace of the mount the inode was created from
* @dir: parent directory inode
@@ -2342,11 +2364,9 @@ umode_t mode_strip_sgid(struct user_namespace *mnt_userns,
return mode;
if (S_ISDIR(mode) || !dir || !(dir->i_mode & S_ISGID))
return mode;
- if (in_group_p(i_gid_into_mnt(mnt_userns, dir)))
+ if (in_group_or_capable(mnt_userns, dir,
+ i_gid_into_mnt(mnt_userns, dir)))
return mode;
- if (capable_wrt_inode_uidgid(mnt_userns, dir, CAP_FSETID))
- return mode;
-
return mode & ~S_ISGID;
}
EXPORT_SYMBOL(mode_strip_sgid);