From: Amir Goldstein amir73il@gmail.com
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 --- 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