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attr: add in_group_or_capable()

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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@gmail.com>
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Amir Goldstein
2023-03-18 12:15:24 +02:00
committed by Greg Kroah-Hartman
parent 94ac142c19
commit 24378d6f74
3 changed files with 27 additions and 10 deletions
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11
fs/attr.c
View File

@@ -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 *dentry, struct iattr *attr)
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, const struct iattr *attr)
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;
}

25
fs/inode.c
View File

@@ -2379,6 +2379,26 @@ int vfs_ioc_fssetxattr_check(struct inode *inode, const struct fsxattr *old_fa,
}
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
@@ -2398,11 +2418,8 @@ umode_t mode_strip_sgid(const struct inode *dir, umode_t mode)
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);

1
fs/internal.h
View File

@@ -149,6 +149,7 @@ extern int vfs_open(const struct path *, struct file *);
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