The patch below does not apply to the 4.19-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 stable@vger.kernel.org.

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-4.19.y git checkout FETCH_HEAD git cherry-pick -x 4f5a100f87f32cb65d4bb1ad282a08c92f6f591e # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2024100136-reanalyze-footwork-21f0@gregkh' --subject-prefix 'PATCH 4.19.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 jannh@google.com 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.

Fixes: 88b88a667971 ("f2fs: support atomic writes") Cc: stable@vger.kernel.org Signed-off-by: Jann Horn jannh@google.com Reviewed-by: Chao Yu chao@kernel.org Reviewed-by: Eric Biggers ebiggers@google.com Signed-off-by: Jaegeuk Kim jaegeuk@kernel.org

diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c index bddcb2cd945a..2c591fbc75a9 100644 --- a/fs/f2fs/file.c +++ b/fs/f2fs/file.c @@ -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;