From: Christian Brauner <brauner@xxxxxxxxxx>
commit 11c2a8700cdcabf9b639b7204a1e38e2a0b6798e upstream.
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@xxxxxxxxx>
Signed-off-by: Christian Brauner (Microsoft) <brauner@xxxxxxxxxx>
Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
---
fs/attr.c | 10 +++++-----
fs/inode.c | 28 ++++++++++++++++++++++++----
fs/internal.h | 2 ++
3 files changed, 31 insertions(+), 9 deletions(-)
diff --git a/fs/attr.c b/fs/attr.c
index 1552a5f23d6b..b1162fca84a2 100644
--- a/fs/attr.c
+++ b/fs/attr.c
@@ -18,6 +18,8 @@
#include <linux/evm.h>
#include <linux/ima.h>
+#include "internal.h"
+
/**
* chown_ok - verify permissions to chown inode
* @mnt_userns: user namespace of the mount @inode was found from
@@ -140,8 +142,7 @@ int setattr_prepare(struct user_namespace *mnt_userns, struct dentry *dentry,
vfsgid = i_gid_into_vfsgid(mnt_userns, inode);
/* Also check the setgid bit! */
- if (!vfsgid_in_group_p(vfsgid) &&
- !capable_wrt_inode_uidgid(mnt_userns, inode, CAP_FSETID))
+ if (!in_group_or_capable(mnt_userns, inode, vfsgid))
attr->ia_mode &= ~S_ISGID;
}
@@ -251,9 +252,8 @@ void setattr_copy(struct user_namespace *mnt_userns, struct inode *inode,
inode->i_ctime = attr->ia_ctime;
if (ia_valid & ATTR_MODE) {
umode_t mode = attr->ia_mode;
- vfsgid_t vfsgid = i_gid_into_vfsgid(mnt_userns, inode);
- if (!vfsgid_in_group_p(vfsgid) &&
- !capable_wrt_inode_uidgid(mnt_userns, inode, CAP_FSETID))
+ if (!in_group_or_capable(mnt_userns, inode,
+ i_gid_into_vfsgid(mnt_userns, inode)))
mode &= ~S_ISGID;
inode->i_mode = mode;
}
diff --git a/fs/inode.c b/fs/inode.c
index b608528efd3a..55299b710c45 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -2487,6 +2487,28 @@ 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
+ * @vfsgid: the new/current vfsgid of @inode
+ *
+ * Check wether @vfsgid 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, vfsgid_t vfsgid)
+{
+ if (vfsgid_in_group_p(vfsgid))
+ 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
@@ -2508,11 +2530,9 @@ 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)))
- return mode;
- if (capable_wrt_inode_uidgid(mnt_userns, dir, CAP_FSETID))
+ if (in_group_or_capable(mnt_userns, dir,
+ i_gid_into_vfsgid(mnt_userns, dir)))
return mode;
-
return mode & ~S_ISGID;
}
EXPORT_SYMBOL(mode_strip_sgid);
diff --git a/fs/internal.h b/fs/internal.h
index 6f0386b34fae..1de39bbc9ddd 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -151,6 +151,8 @@ extern int vfs_open(const struct path *, struct file *);
*/
extern long prune_icache_sb(struct super_block *sb, struct shrink_control *sc);
extern int dentry_needs_remove_privs(struct dentry *dentry);
+bool in_group_or_capable(struct user_namespace *mnt_userns,
+ const struct inode *inode, vfsgid_t vfsgid);
/*
* fs-writeback.c
--
2.34.1
