From: Eric Biggers <ebiggers@google.com>
Date: Thu, 6 Apr 2023 14:31:11 -0700
Subject: [PATCH] fsverity: reject FS_IOC_ENABLE_VERITY on mode 3 fds
References: bsc#1012628
Patch-mainline: 6.3.1
Git-commit: 04839139213cf60d4c5fc792214a08830e294ff8
commit 04839139213cf60d4c5fc792214a08830e294ff8 upstream.
Commit 56124d6c87fd ("fsverity: support enabling with tree block size <
PAGE_SIZE") changed FS_IOC_ENABLE_VERITY to use __kernel_read() to read
the file's data, instead of direct pagecache accesses.
An unintended consequence of this is that the
'WARN_ON_ONCE(!(file->f_mode & FMODE_READ))' in __kernel_read() became
reachable by fuzz tests. This happens if FS_IOC_ENABLE_VERITY is called
on a fd opened with access mode 3, which means "ioctl access only".
Arguably, FS_IOC_ENABLE_VERITY should work on ioctl-only fds. But
ioctl-only fds are a weird Linux extension that is rarely used and that
few people even know about. (The documentation for FS_IOC_ENABLE_VERITY
even specifically says it requires O_RDONLY.) It's probably not
worthwhile to make the ioctl internally open a new fd just to handle
this case. Thus, just reject the ioctl on such fds for now.
Fixes: 56124d6c87fd ("fsverity: support enabling with tree block size < PAGE_SIZE")
Reported-by: syzbot+51177e4144d764827c45@syzkaller.appspotmail.com
Link: https://syzkaller.appspot.com/bug?id=2281afcbbfa8fdb92f9887479cc0e4180f1c6b28
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20230406215106.235829-1-ebiggers@kernel.org
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
fs/verity/enable.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/fs/verity/enable.c b/fs/verity/enable.c
index 7a0e3a84..4abbd7c9 100644
--- a/fs/verity/enable.c
+++ b/fs/verity/enable.c
@@ -347,6 +347,13 @@ int fsverity_ioctl_enable(struct file *filp, const void __user *uarg)
err = file_permission(filp, MAY_WRITE);
if (err)
return err;
+ /*
+ * __kernel_read() is used while building the Merkle tree. So, we can't
+ * allow file descriptors that were opened for ioctl access only, using
+ * the special nonstandard access mode 3. O_RDONLY only, please!
+ */
+ if (!(filp->f_mode & FMODE_READ))
+ return -EBADF;
if (IS_APPEND(inode))
return -EPERM;
--
2.35.3