The patch titled Subject: mm: avoid overflows in dirty throttling logic has been added to the -mm mm-unstable branch. Its filename is mm-avoid-overflows-in-dirty-throttling-logic.patch
This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...
This patch will later appear in the mm-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------ From: Jan Kara jack@suse.cz Subject: mm: avoid overflows in dirty throttling logic Date: Fri, 21 Jun 2024 16:42:38 +0200
The dirty throttling logic is interspersed with assumptions that dirty limits in PAGE_SIZE units fit into 32-bit (so that various multiplications fit into 64-bits). If limits end up being larger, we will hit overflows, possible divisions by 0 etc. Fix these problems by never allowing so large dirty limits as they have dubious practical value anyway. For dirty_bytes / dirty_background_bytes interfaces we can just refuse to set so large limits. For dirty_ratio / dirty_background_ratio it isn't so simple as the dirty limit is computed from the amount of available memory which can change due to memory hotplug etc. So when converting dirty limits from ratios to numbers of pages, we just don't allow the result to exceed UINT_MAX.
Link: https://lkml.kernel.org/r/20240621144246.11148-2-jack@suse.cz Signed-off-by: Jan Kara jack@suse.cz Reported-by: Zach O'Keefe zokeefe@google.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---
mm/page-writeback.c | 30 ++++++++++++++++++++++++++---- 1 file changed, 26 insertions(+), 4 deletions(-)
--- a/mm/page-writeback.c~mm-avoid-overflows-in-dirty-throttling-logic +++ a/mm/page-writeback.c @@ -417,13 +417,20 @@ static void domain_dirty_limits(struct d else bg_thresh = (bg_ratio * available_memory) / PAGE_SIZE;
- if (bg_thresh >= thresh) - bg_thresh = thresh / 2; tsk = current; if (rt_task(tsk)) { bg_thresh += bg_thresh / 4 + global_wb_domain.dirty_limit / 32; thresh += thresh / 4 + global_wb_domain.dirty_limit / 32; } + /* + * Dirty throttling logic assumes the limits in page units fit into + * 32-bits. This gives 16TB dirty limits max which is hopefully enough. + */ + if (thresh > UINT_MAX) + thresh = UINT_MAX; + /* This makes sure bg_thresh is within 32-bits as well */ + if (bg_thresh >= thresh) + bg_thresh = thresh / 2; dtc->thresh = thresh; dtc->bg_thresh = bg_thresh;
@@ -473,7 +480,11 @@ static unsigned long node_dirty_limit(st if (rt_task(tsk)) dirty += dirty / 4;
- return dirty; + /* + * Dirty throttling logic assumes the limits in page units fit into + * 32-bits. This gives 16TB dirty limits max which is hopefully enough. + */ + return min_t(unsigned long, dirty, UINT_MAX); }
/** @@ -510,10 +521,17 @@ static int dirty_background_bytes_handle void *buffer, size_t *lenp, loff_t *ppos) { int ret; + unsigned long old_bytes = dirty_background_bytes;
ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos); - if (ret == 0 && write) + if (ret == 0 && write) { + if (DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE) > + UINT_MAX) { + dirty_background_bytes = old_bytes; + return -ERANGE; + } dirty_background_ratio = 0; + } return ret; }
@@ -539,6 +557,10 @@ static int dirty_bytes_handler(struct ct
ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos); if (ret == 0 && write && vm_dirty_bytes != old_bytes) { + if (DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE) > UINT_MAX) { + vm_dirty_bytes = old_bytes; + return -ERANGE; + } writeback_set_ratelimit(); vm_dirty_ratio = 0; } _
Patches currently in -mm which might be from jack@suse.cz are
ocfs2-fix-dio-failure-due-to-insufficient-transaction-credits.patch revert-mm-writeback-fix-possible-divide-by-zero-in-wb_dirty_limits-again.patch mm-avoid-overflows-in-dirty-throttling-logic.patch