From: Zach O'Keefe zokeefe@google.com

stable inclusion from stable-v5.10.210 commit 81e7d2530d458548b90a5c5e76b77ad5e5d1c0df category: bugfix bugzilla: https://gitee.com/src-openeuler/kernel/issues/I9E2EC

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=...

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commit 9319b647902cbd5cc884ac08a8a6d54ce111fc78 upstream.

(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@google.com Fixes: f6789593d5ce ("mm/page-writeback.c: fix divide by zero in bdi_dirty_limits()") Signed-off-by: Zach O'Keefe zokeefe@google.com Cc: Maxim Patlasov MPatlasov@parallels.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Wang Hai wanghai38@huawei.com --- mm/page-writeback.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/page-writeback.c b/mm/page-writeback.c index b72da123f242..e969667e8d62 100644 --- a/mm/page-writeback.c +++ b/mm/page-writeback.c @@ -1519,7 +1519,7 @@ static inline void wb_dirty_limits(struct dirty_throttle_control *dtc) */ 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