FAILED: patch "[PATCH] f2fs: Require FMODE_WRITE for atomic write ioctls" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x 4f5a100f87f32cb65d4bb1ad282a08c92f6f591e
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2024100133-islamic-matriarch-4cee@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:

4f5a100f87f3 ("f2fs: Require FMODE_WRITE for atomic write ioctls")
01beba7957a2 ("fs: port inode_owner_or_capable() to mnt_idmap")
f2d40141d5d9 ("fs: port inode_init_owner() to mnt_idmap")
4609e1f18e19 ("fs: port ->permission() to pass mnt_idmap")
8782a9aea3ab ("fs: port ->fileattr_set() to pass mnt_idmap")
13e83a4923be ("fs: port ->set_acl() to pass mnt_idmap")
77435322777d ("fs: port ->get_acl() to pass mnt_idmap")
011e2b717b1b ("fs: port ->tmpfile() to pass mnt_idmap")
5ebb29bee8d5 ("fs: port ->mknod() to pass mnt_idmap")
c54bd91e9eab ("fs: port ->mkdir() to pass mnt_idmap")
7a77db95511c ("fs: port ->symlink() to pass mnt_idmap")
6c960e68aaed ("fs: port ->create() to pass mnt_idmap")
b74d24f7a74f ("fs: port ->getattr() to pass mnt_idmap")
c1632a0f1120 ("fs: port ->setattr() to pass mnt_idmap")
abf08576afe3 ("fs: port vfs_*() helpers to struct mnt_idmap")
6022ec6ee2c3 ("Merge tag 'ntfs3_for_6.2' of https://github.com/Paragon-Software-Group/linux-ntfs3")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 4f5a100f87f32cb65d4bb1ad282a08c92f6f591e Mon Sep 17 00:00:00 2001
From: Jann Horn <[email protected]>
Date: Tue, 6 Aug 2024 16:07:16 +0200
Subject: [PATCH] f2fs: Require FMODE_WRITE for atomic write ioctls

The F2FS ioctls for starting and committing atomic writes check for inode_owner_or_capable(), but this does not give LSMs like SELinux or Landlock an opportunity to deny the write access - if the caller's FSUID matches the inode's UID, inode_owner_or_capable() immediately returns true.

There are scenarios where LSMs want to deny a process the ability to write particular files, even files that the FSUID of the process owns; but this can currently partially be bypassed using atomic write ioctls in two ways:

- F2FS_IOC_START_ATOMIC_REPLACE + F2FS_IOC_COMMIT_ATOMIC_WRITE can truncate an inode to size 0
- F2FS_IOC_START_ATOMIC_WRITE + F2FS_IOC_ABORT_ATOMIC_WRITE can revert changes another process concurrently made to a file

Fix it by requiring FMODE_WRITE for these operations, just like for F2FS_IOC_MOVE_RANGE. Since any legitimate caller should only be using these ioctls when intending to write into the file, that seems unlikely to break anything.

index bddcb2cd945a..2c591fbc75a9 100644
@@ -2131,6 +2131,9 @@ static int f2fs_ioc_start_atomic_write(struct file *filp, bool truncate)
 	loff_t isize;
 	int ret;
 
+	if (!(filp->f_mode & FMODE_WRITE))
+		return -EBADF;
+
 	if (!inode_owner_or_capable(idmap, inode))
 		return -EACCES;
 

@@ -2239,6 +2242,9 @@ static int f2fs_ioc_commit_atomic_write(struct file *filp)
 	struct mnt_idmap *idmap = file_mnt_idmap(filp);
 	int ret;
 
+	if (!(filp->f_mode & FMODE_WRITE))
+		return -EBADF;
+
 	if (!inode_owner_or_capable(idmap, inode))
 		return -EACCES;
 

@@ -2271,6 +2277,9 @@ static int f2fs_ioc_abort_atomic_write(struct file *filp)
 	struct mnt_idmap *idmap = file_mnt_idmap(filp);
 	int ret;
 
+	if (!(filp->f_mode & FMODE_WRITE))
+		return -EBADF;
+
 	if (!inode_owner_or_capable(idmap, inode))
 		return -EACCES;