This is a note to let you know that I've just added the patch titled
bcache: prevent potential division by zero error
to the 4.19-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
bcache-prevent-potential-division-by-zero-error.patch
and it can be found in the queue-4.19 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 2c7f497ac274a14330208b18f6f734000868ebf9 Mon Sep 17 00:00:00 2001
From: Rand Deeb <rand.sec96@xxxxxxxxx>
Date: Mon, 20 Nov 2023 13:24:57 +0800
Subject: bcache: prevent potential division by zero error
From: Rand Deeb <rand.sec96@xxxxxxxxx>
commit 2c7f497ac274a14330208b18f6f734000868ebf9 upstream.
In SHOW(), the variable 'n' is of type 'size_t.' While there is a
conditional check to verify that 'n' is not equal to zero before
executing the 'do_div' macro, concerns arise regarding potential
division by zero error in 64-bit environments.
The concern arises when 'n' is 64 bits in size, greater than zero, and
the lower 32 bits of it are zeros. In such cases, the conditional check
passes because 'n' is non-zero, but the 'do_div' macro casts 'n' to
'uint32_t,' effectively truncating it to its lower 32 bits.
Consequently, the 'n' value becomes zero.
To fix this potential division by zero error and ensure precise
division handling, this commit replaces the 'do_div' macro with
div64_u64(). div64_u64() is designed to work with 64-bit operands,
guaranteeing that division is performed correctly.
This change enhances the robustness of the code, ensuring that division
operations yield accurate results in all scenarios, eliminating the
possibility of division by zero, and improving compatibility across
different 64-bit environments.
Found by Linux Verification Center (linuxtesting.org) with SVACE.
Signed-off-by: Rand Deeb <rand.sec96@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Coly Li <colyli@xxxxxxx>
Link: https://lore.kernel.org/r/20231120052503.6122-5-colyli@xxxxxxx
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/md/bcache/sysfs.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/drivers/md/bcache/sysfs.c
+++ b/drivers/md/bcache/sysfs.c
@@ -992,7 +992,7 @@ SHOW(__bch_cache)
sum += INITIAL_PRIO - cached[i];
if (n)
- do_div(sum, n);
+ sum = div64_u64(sum, n);
for (i = 0; i < ARRAY_SIZE(q); i++)
q[i] = INITIAL_PRIO - cached[n * (i + 1) /
Patches currently in stable-queue which might be from rand.sec96@xxxxxxxxx are
queue-4.19/bcache-prevent-potential-division-by-zero-error.patch
