4.14-stable review patch. If anyone has any objections, please let me know.
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From: Rand Deeb rand.sec96@gmail.com
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@gmail.com Cc: stable@vger.kernel.org Signed-off-by: Coly Li colyli@suse.de Link: https://lore.kernel.org/r/20231120052503.6122-5-colyli@suse.de Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- 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 @@ -831,7 +831,7 @@ 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) /