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| author | Eric Biggers <ebiggers@google.com> | 2023-04-06 23:31:11 +0200 |
|---|---|---|
| committer | Eric Biggers <ebiggers@google.com> | 2023-04-12 04:23:23 +0200 |
| commit | 04839139213cf60d4c5fc792214a08830e294ff8 (patch) | |
| tree | 8485c656890a7ee4ea4d4cbc170b893b024f9470 /fs/verity | |
| parent | fsverity: explicitly check for buffer overflow in build_merkle_tree() (diff) | |
| download | linux-04839139213cf60d4c5fc792214a08830e294ff8.tar.xz linux-04839139213cf60d4c5fc792214a08830e294ff8.zip | |
fsverity: reject FS_IOC_ENABLE_VERITY on mode 3 fds
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>
Diffstat (limited to 'fs/verity')
| -rw-r--r-- | fs/verity/enable.c | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/fs/verity/enable.c b/fs/verity/enable.c index bbec6f93172c..fc4c50e5219d 100644 --- a/fs/verity/enable.c +++ b/fs/verity/enable.c @@ -357,6 +357,13 @@ 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; |