Merge tag 'execve-v6.11-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux

Pull execve fixes from Kees Cook:

 - binfmt_flat: Fix corruption when not offsetting data start

 - exec: Fix ToCToU between perm check and set-uid/gid usage

* tag 'execve-v6.11-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux:
  exec: Fix ToCToU between perm check and set-uid/gid usage
  binfmt_flat: Fix corruption when not offsetting data start

fs/binfmt_flat.c

@@ -72,8 +72,10 @@
 
 #ifdef CONFIG_BINFMT_FLAT_NO_DATA_START_OFFSET
 #define DATA_START_OFFSET_WORDS		(0)
+#define MAX_SHARED_LIBS_UPDATE		(0)
 #else
 #define DATA_START_OFFSET_WORDS		(MAX_SHARED_LIBS)
+#define MAX_SHARED_LIBS_UPDATE		(MAX_SHARED_LIBS)
 #endif
 
 struct lib_info {
@@ -880,7 +882,7 @@ static int load_flat_binary(struct linux_binprm *bprm)
 		return res;
 
 	/* Update data segment pointers for all libraries */
-	for (i = 0; i < MAX_SHARED_LIBS; i++) {
+	for (i = 0; i < MAX_SHARED_LIBS_UPDATE; i++) {
 		if (!libinfo.lib_list[i].loaded)
 			continue;
 		for (j = 0; j < MAX_SHARED_LIBS; j++) {

fs/exec.c

@@ -1692,6 +1692,7 @@ static void bprm_fill_uid(struct linux_binprm *bprm, struct file *file)
 	unsigned int mode;
 	vfsuid_t vfsuid;
 	vfsgid_t vfsgid;
+	int err;
 
 	if (!mnt_may_suid(file->f_path.mnt))
 		return;
@@ -1708,12 +1709,17 @@ static void bprm_fill_uid(struct linux_binprm *bprm, struct file *file)
 	/* Be careful if suid/sgid is set */
 	inode_lock(inode);
 
-	/* reload atomically mode/uid/gid now that lock held */
+	/* Atomically reload and check mode/uid/gid now that lock held. */
 	mode = inode->i_mode;
 	vfsuid = i_uid_into_vfsuid(idmap, inode);
 	vfsgid = i_gid_into_vfsgid(idmap, inode);
+	err = inode_permission(idmap, inode, MAY_EXEC);
 	inode_unlock(inode);
 
+	/* Did the exec bit vanish out from under us? Give up. */
+	if (err)
+		return;
+
 	/* We ignore suid/sgid if there are no mappings for them in the ns */
 	if (!vfsuid_has_mapping(bprm->cred->user_ns, vfsuid) ||
 	    !vfsgid_has_mapping(bprm->cred->user_ns, vfsgid))