linux-kernel - [PATCH] fork: Replace simple_strtoul with kstrtoul in coredump_filter

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Message-ID: <20251215142152.4082-2-thorsten.blum@linux.dev>
Date: Mon, 15 Dec 2025 15:21:52 +0100
From: Thorsten Blum <thorsten.blum@...ux.dev>
To: Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>,
	Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Hildenbrand <david@...nel.org>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Mike Rapoport <rppt@...nel.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Michal Hocko <mhocko@...e.com>,
	Kees Cook <kees@...nel.org>
Cc: Thorsten Blum <thorsten.blum@...ux.dev>,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] fork: Replace simple_strtoul with kstrtoul in coredump_filter_setup

Replace simple_strtoul() with the recommended kstrtoul() for parsing the
'coredump_filter=' boot parameter.

Check the return value of kstrtoul() and reject invalid values. This
adds error handling while preserving behavior for existing values, and
removes use of the deprecated simple_strtoul() helper. The current code
silently sets 'default_dump_filter = 0' if parsing fails, instead of
leaving the default value (MMF_DUMP_FILTER_DEFAULT) unchanged.

Rename the static variable 'default_dump_filter' to 'coredump_filter'
since it does not necessarily contain the default value and the current
name can be misleading.

Signed-off-by: Thorsten Blum <thorsten.blum@...ux.dev>
---
 kernel/fork.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/kernel/fork.c b/kernel/fork.c
index b1f3915d5f8e..f33ee7fe53ad 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1012,13 +1012,14 @@ static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
 
 __cacheline_aligned_in_smp DEFINE_SPINLOCK(mmlist_lock);
 
-static unsigned long default_dump_filter = MMF_DUMP_FILTER_DEFAULT;
+static unsigned long coredump_filter = MMF_DUMP_FILTER_DEFAULT;
 
 static int __init coredump_filter_setup(char *s)
 {
-	default_dump_filter =
-		(simple_strtoul(s, NULL, 0) << MMF_DUMP_FILTER_SHIFT) &
-		MMF_DUMP_FILTER_MASK;
+	if (kstrtoul(s, 0, &coredump_filter))
+		return 0;
+	coredump_filter <<= MMF_DUMP_FILTER_SHIFT;
+	coredump_filter &= MMF_DUMP_FILTER_MASK;
 	return 1;
 }
 
@@ -1104,7 +1105,7 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p,
 		__mm_flags_overwrite_word(mm, mmf_init_legacy_flags(flags));
 		mm->def_flags = current->mm->def_flags & VM_INIT_DEF_MASK;
 	} else {
-		__mm_flags_overwrite_word(mm, default_dump_filter);
+		__mm_flags_overwrite_word(mm, coredump_filter);
 		mm->def_flags = 0;
 	}
 
-- 
Thorsten Blum <thorsten.blum@...ux.dev>
GPG: 1D60 735E 8AEF 3BE4 73B6  9D84 7336 78FD 8DFE EAD4