From: Amir Goldstein <amir73il@xxxxxxxxx>
commit 11c2a8700cdcabf9b639b7204a1e38e2a0b6798e upstream.
[backported to 5.10.y, prior to idmapped mounts]
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/attr.c | 11 +++++------
fs/inode.c | 25 +++++++++++++++++++++----
fs/internal.h | 1 +
3 files changed, 27 insertions(+), 10 deletions(-)
--- a/fs/attr.c
+++ b/fs/attr.c
@@ -18,6 +18,8 @@
#include <linux/evm.h>
#include <linux/ima.h>
+#include "internal.h"
+
static bool chown_ok(const struct inode *inode, kuid_t uid)
{
if (uid_eq(current_fsuid(), inode->i_uid) &&
@@ -90,9 +92,8 @@ int setattr_prepare(struct dentry *dentr
if (!inode_owner_or_capable(inode))
return -EPERM;
/* Also check the setgid bit! */
- if (!in_group_p((ia_valid & ATTR_GID) ? attr->ia_gid :
- inode->i_gid) &&
- !capable_wrt_inode_uidgid(inode, CAP_FSETID))
+ if (!in_group_or_capable(inode, (ia_valid & ATTR_GID) ?
+ attr->ia_gid : inode->i_gid))
attr->ia_mode &= ~S_ISGID;
}
@@ -193,9 +194,7 @@ void setattr_copy(struct inode *inode, c
inode->i_ctime = attr->ia_ctime;
if (ia_valid & ATTR_MODE) {
umode_t mode = attr->ia_mode;
-
- if (!in_group_p(inode->i_gid) &&
- !capable_wrt_inode_uidgid(inode, CAP_FSETID))
+ if (!in_group_or_capable(inode, inode->i_gid))
mode &= ~S_ISGID;
inode->i_mode = mode;
}
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -2380,6 +2380,26 @@ int vfs_ioc_fssetxattr_check(struct inod
EXPORT_SYMBOL(vfs_ioc_fssetxattr_check);
/**
+ * in_group_or_capable - check whether caller is CAP_FSETID privileged
+ * @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(const struct inode *inode, kgid_t gid)
+{
+ if (in_group_p(gid))
+ return true;
+ if (capable_wrt_inode_uidgid(inode, CAP_FSETID))
+ return true;
+ return false;
+}
+
+/**
* mode_strip_sgid - handle the sgid bit for non-directories
* @dir: parent directory inode
* @mode: mode of the file to be created in @dir
@@ -2398,11 +2418,8 @@ umode_t mode_strip_sgid(const struct ino
return mode;
if (S_ISDIR(mode) || !dir || !(dir->i_mode & S_ISGID))
return mode;
- if (in_group_p(dir->i_gid))
+ if (in_group_or_capable(dir, dir->i_gid))
return mode;
- if (capable_wrt_inode_uidgid(dir, CAP_FSETID))
- return mode;
-
return mode & ~S_ISGID;
}
EXPORT_SYMBOL(mode_strip_sgid);
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -149,6 +149,7 @@ extern int vfs_open(const struct path *,
extern long prune_icache_sb(struct super_block *sb, struct shrink_control *sc);
extern void inode_add_lru(struct inode *inode);
extern int dentry_needs_remove_privs(struct dentry *dentry);
+bool in_group_or_capable(const struct inode *inode, kgid_t gid);
/*
* fs-writeback.c
