[PATCH v3 2/8] mm: userfaultfd: check for start + len overflow in validate_range

Axel Rasmussen
2023-07-06T22:51:05Z

Most userfaultfd ioctls take a `start + len` range as an argument.
We have the validate_range helper to check that such ranges are valid.
However, some (but not all!) ioctls *also* check that `start + len`
doesn't wrap around (overflow).

Just check for this in validate_range. This saves some repetitive code,
and adds the check to some ioctls which weren't bothering to check for
it before.

Signed-off-by: Axel Rasmussen <axelrasmussen@google.com>
---
fs/userfaultfd.c | 15 +++------------
1 file changed, 3 insertions(+), 12 deletions(-)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 7cecd49e078b..2e84684c46f0 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -1306,6 +1306,8 @@ static __always_inline int validate_range(struct mm_struct *mm,
return -EINVAL;
if (len > task_size - start)
return -EINVAL;
+ if (start + len <= start)
+ return -EINVAL;
return 0;
}

@@ -1760,14 +1762,8 @@ static int userfaultfd_copy(struct userfaultfd_ctx *ctx,
ret = validate_range(ctx->mm, uffdio_copy.dst, uffdio_copy.len);
if (ret)
goto out;
- /*
- * double check for wraparound just in case. copy_from_user()
- * will later check uffdio_copy.src + uffdio_copy.len to fit
- * in the userland range.
- */
+
ret = -EINVAL;
- if (uffdio_copy.src + uffdio_copy.len <= uffdio_copy.src)
- goto out;
if (uffdio_copy.mode & ~(UFFDIO_COPY_MODE_DONTWAKE|UFFDIO_COPY_MODE_WP))
goto out;
if (uffdio_copy.mode & UFFDIO_COPY_MODE_WP)
@@ -1927,11 +1923,6 @@ static int userfaultfd_continue(struct userfaultfd_ctx *ctx, unsigned long arg)
goto out;

ret = -EINVAL;
- /* double check for wraparound just in case. */
- if (uffdio_continue.range.start + uffdio_continue.range.len <=
- uffdio_continue.range.start) {
- goto out;
- }
if (uffdio_continue.mode & ~(UFFDIO_CONTINUE_MODE_DONTWAKE |
UFFDIO_CONTINUE_MODE_WP))
goto out;
--
2.41.0.255.g8b1d071c50-goog