The patch titled
Subject: mm/writeback: fix possible divide-by-zero in wb_dirty_limits(), again
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
mm-writeback-fix-possible-divide-by-zero-in-wb_dirty_limits-again.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-writeback-fix-possible-divide-by-zero-in-wb_dirty_limits-again.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: "Zach O'Keefe" <zokeefe@xxxxxxxxxx>
Subject: mm/writeback: fix possible divide-by-zero in wb_dirty_limits(), again
Date: Thu, 18 Jan 2024 10:19:53 -0800
(struct dirty_throttle_control *)->thresh is an unsigned long, but is
passed as the u32 divisor argument to div_u64(). On architectures where
unsigned long is 64 bytes, the argument will be implicitly truncated.
Use div64_u64() instead of div_u64() so that the value used in the "is
this a safe division" check is the same as the divisor.
Also, remove redundant cast of the numerator to u64, as that should happen
implicitly.
This would be difficult to exploit in memcg domain, given the ratio-based
arithmetic domain_drity_limits() uses, but is much easier in global
writeback domain with a BDI_CAP_STRICTLIMIT-backing device, using e.g.
vm.dirty_bytes=(1<<32)*PAGE_SIZE so that dtc->thresh == (1<<32)
Link: https://lkml.kernel.org/r/20240118181954.1415197-1-zokeefe@xxxxxxxxxx
Fixes: f6789593d5ce ("mm/page-writeback.c: fix divide by zero in bdi_dirty_limits()")
Signed-off-by: Zach O'Keefe <zokeefe@xxxxxxxxxx>
Cc: Maxim Patlasov <MPatlasov@xxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page-writeback.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/mm/page-writeback.c~mm-writeback-fix-possible-divide-by-zero-in-wb_dirty_limits-again
+++ a/mm/page-writeback.c
@@ -1638,7 +1638,7 @@ static inline void wb_dirty_limits(struc
*/
dtc->wb_thresh = __wb_calc_thresh(dtc);
dtc->wb_bg_thresh = dtc->thresh ?
- div_u64((u64)dtc->wb_thresh * dtc->bg_thresh, dtc->thresh) : 0;
+ div64_u64(dtc->wb_thresh * dtc->bg_thresh, dtc->thresh) : 0;
/*
* In order to avoid the stacked BDI deadlock we need
_
Patches currently in -mm which might be from zokeefe@xxxxxxxxxx are
mm-writeback-fix-possible-divide-by-zero-in-wb_dirty_limits-again.patch
