On 12/22/23 8:23 AM, Ilya Dryomov wrote:
On Thu, Dec 21, 2023 at 2:40 PM Dmitry Antipov <dmantipov@xxxxxxxxx> wrote:
When compiling with clang-18 and W=1, I've noticed the following
warning:
drivers/block/rbd.c:6093:17: warning: result of comparison of constant
2305843009213693948 with expression of type 'u32' (aka 'unsigned int')
is always false [-Wtautological-constant-out-of-range-compare]
6093 | if (snap_count > (SIZE_MAX - sizeof (struct ceph_snap_context))
| ~~~~~~~~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
6094 | / sizeof (u64)) {
| ~~~~~~~~~~~~~~
Since the plain check with '>' makes sense only if U32_MAX == SIZE_MAX
which is not true for the 64-bit kernel, prefer 'check_sub_overflow()'
in 'rbd_dev_v2_snap_context()' and 'rbd_dev_ondisk_valid()' as well.
Signed-off-by: Dmitry Antipov <dmantipov@xxxxxxxxx>
---
drivers/block/rbd.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index a999b698b131..ef8e6fbc9a79 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -933,7 +933,7 @@ static bool rbd_image_format_valid(u32 image_format)
static bool rbd_dev_ondisk_valid(struct rbd_image_header_ondisk *ondisk)
{
- size_t size;
+ size_t size, result;
u32 snap_count;
/* The header has to start with the magic rbd header text */
@@ -956,7 +956,7 @@ static bool rbd_dev_ondisk_valid(struct rbd_image_header_ondisk *ondisk)
*/
snap_count = le32_to_cpu(ondisk->snap_count);
size = SIZE_MAX - sizeof (struct ceph_snap_context);
- if (snap_count > size / sizeof (__le64))
+ if (check_sub_overflow(size / sizeof(__le64), snap_count, &result))
Hi Dmitry,
There is a limit on the number of snapshots:
#define RBD_MAX_SNAP_COUNT 510 /* allows max snapc to fit in 4KB */
It's not direct, but it's a hard limit, at least in the current
implementation. Let's just replace these with direct comparisons for
RBD_MAX_SNAP_COUNT.
The point of the original code was to ensure the on-disk snap_count
value was sane, but there's no point in checking for a 64-bit size_t.
Comparing against RBD_MAX_SNAP_COUNT is better. I think it's safe
to assume RBD_MAX_SNAP_COUNT (or rather, the size required to hold
that many snapshot IDs) can always be represented in a size_t.
-Alex
Thanks,
Ilya
