From: Christian Brauner brauner@kernel.org
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 --- fs/attr.c | 8 ++++---- fs/inode.c | 28 ++++++++++++++++++++++++---- fs/internal.h | 2 ++ 3 files changed, 30 insertions(+), 8 deletions(-)
diff --git a/fs/attr.c b/fs/attr.c index f581c4d008971..686840aa91c8b 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 @@ -141,8 +143,7 @@ int setattr_prepare(struct user_namespace *mnt_userns, struct dentry *dentry, mapped_gid = i_gid_into_mnt(mnt_userns, inode);
/* Also check the setgid bit! */ - if (!in_group_p(mapped_gid) && - !capable_wrt_inode_uidgid(mnt_userns, inode, CAP_FSETID)) + if (!in_group_or_capable(mnt_userns, inode, mapped_gid)) attr->ia_mode &= ~S_ISGID; }
@@ -257,8 +258,7 @@ void setattr_copy(struct user_namespace *mnt_userns, struct inode *inode, if (ia_valid & ATTR_MODE) { umode_t mode = attr->ia_mode; kgid_t kgid = i_gid_into_mnt(mnt_userns, inode); - if (!in_group_p(kgid) && - !capable_wrt_inode_uidgid(mnt_userns, inode, CAP_FSETID)) + if (!in_group_or_capable(mnt_userns, inode, kgid)) mode &= ~S_ISGID; inode->i_mode = mode; } diff --git a/fs/inode.c b/fs/inode.c index 957b2d18ec29f..a71fb82279bb1 100644 --- a/fs/inode.c +++ b/fs/inode.c @@ -2321,6 +2321,28 @@ 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 @@ -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))) - return mode; - if (capable_wrt_inode_uidgid(mnt_userns, dir, CAP_FSETID)) + if (in_group_or_capable(mnt_userns, dir, + i_gid_into_mnt(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 9075490f21a62..c898147272817 100644 --- a/fs/internal.h +++ b/fs/internal.h @@ -150,6 +150,8 @@ 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(struct user_namespace *mnt_userns, + const struct inode *inode, kgid_t gid);
/* * fs-writeback.c