NFS server is exporting a sticky directory (mode 01777) with root squashing enabled. Client has protect_regular enabled and then tries to open a file as root in that directory. File is created (with ownership set to nobody:nobody) but the open syscall returns an error. The problem is may_create_in_sticky, which rejects the open even though the file has already been created/opened. Bypass the checks in may_create_in_sticky if the task has CAP_FOWNER in the given namespace. Link: https://bugzilla.redhat.com/show_bug.cgi?id=1976829 Reported-by: Yongchen Yang <yoyang@xxxxxxxxxx> Suggested-by: Christian Brauner <brauner@xxxxxxxxxx> Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx> --- fs/namei.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/fs/namei.c b/fs/namei.c index 1f28d3f463c3..170c2396ba29 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -1230,7 +1230,8 @@ static int may_create_in_sticky(struct user_namespace *mnt_userns, (!sysctl_protected_regular && S_ISREG(inode->i_mode)) || likely(!(dir_mode & S_ISVTX)) || uid_eq(i_uid_into_mnt(mnt_userns, inode), dir_uid) || - uid_eq(current_fsuid(), i_uid_into_mnt(mnt_userns, inode))) + uid_eq(current_fsuid(), i_uid_into_mnt(mnt_userns, inode)) || + ns_capable(mnt_userns, CAP_FOWNER)) return 0; if (likely(dir_mode & 0002) || -- 2.37.1
