On Fri, Oct 04, 2024 at 07:34:41PM +0000, Eric Biggers wrote:
From: Jann Horn <ja...@google.com>commit 4f5a100f87f32cb65d4bb1ad282a08c92f6f591e upstream. 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: sta...@vger.kernel.org Signed-off-by: Jann Horn <ja...@google.com> Reviewed-by: Chao Yu <c...@kernel.org> Reviewed-by: Eric Biggers <ebigg...@google.com> Signed-off-by: Jaegeuk Kim <jaeg...@kernel.org> Signed-off-by: Eric Biggers <ebigg...@google.com>
I've queued these backports, thanks! -- Thanks, Sasha _______________________________________________ Linux-f2fs-devel mailing list Linux-f2fs-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
