From: Christian Brauner brauner@kernel.org
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@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 --- fs/attr.c | 10 +++++----- fs/inode.c | 28 ++++++++++++++++++++++++---- fs/internal.h | 2 ++ 3 files changed, 31 insertions(+), 9 deletions(-)
--- 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_namespac 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 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; } --- a/fs/inode.c +++ b/fs/inode.c @@ -2488,6 +2488,28 @@ struct timespec64 current_time(struct in 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 * @dir: parent directory inode @@ -2508,11 +2530,9 @@ umode_t mode_strip_sgid(struct user_name 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_vfsgid(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); --- a/fs/internal.h +++ b/fs/internal.h @@ -151,6 +151,8 @@ extern int vfs_open(const struct path *, */ 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