[PATCH] fs/coredump: reduce redundant log noise in validate_coredump_safety

[lirongqing <lirongqing@baidu.com>]

From: Li RongQing <lirongqing@baidu.com>

Currently, writing to 'core_pattern' or 'suid_dumpable' sysctl nodes
always triggers validate_coredump_safety(), even if the values have
not changed. This results in redundant warning messages in dmesg:

"Unsafe core_pattern used with fs.suid_dumpable=2..."

This patch optimizes the procfs handlers to only invoke the safety
validation when an actual change in the configuration is detected:

1. In proc_dostring_coredump(), compare the new core_pattern string
   with the existing one using strncmp().
2. In proc_dointvec_minmax_coredump(), check if the new suid_dumpable
   value differs from the previous one.

This keeps the kernel log clean from repetitive warnings when
re-applying the same sysctl settings.

Signed-off-by: Li RongQing <lirongqing@baidu.com>
---
 fs/coredump.c | 3 ++-
 fs/exec.c     | 6 ++++--
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/fs/coredump.c b/fs/coredump.c
index 29df8aa..9b357d2 100644
--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -1483,7 +1483,8 @@ static int proc_dostring_coredump(const struct ctl_table *table, int write,
 		return -EINVAL;
 	}
 
-	validate_coredump_safety();
+	if (strncmp(old_core_pattern, core_pattern, CORENAME_MAX_SIZE))
+		validate_coredump_safety();
 	return error;
 }
 
diff --git a/fs/exec.c b/fs/exec.c
index 9ea3a77..32b46e4 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1975,9 +1975,11 @@ COMPAT_SYSCALL_DEFINE5(execveat, int, fd,
 static int proc_dointvec_minmax_coredump(const struct ctl_table *table, int write,
 		void *buffer, size_t *lenp, loff_t *ppos)
 {
-	int error = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
+	int error, old = READ_ONCE(suid_dumpable);
 
-	if (!error && write)
+	error = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
+
+	if (!error && write && (old != READ_ONCE(suid_dumpable)))
 		validate_coredump_safety();
 	return error;
 }
-- 
2.9.4