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.

Link: https://lkml.kernel.org/r/20251215142152.4082-2-thorsten.blum@linux.dev
Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Ben Segall <bsegall@google.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Kees Cook <kees@kernel.org>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 6 insertions, 5 deletions

diff --git a/kernel/fork.c b/kernel/fork.c
index 1ec0caea6a7e..db02a301d0c0 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1014,13 +1014,14 @@ free_tsk:
 
 __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;
 }
 
@@ -1106,7 +1107,7 @@ 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;
 	}