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

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

[lirongqing]

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

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

[Li,Rongqing(ACG CCN)]

> 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

Ping 
Thanks

[Li,Rongqing] 

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

[Christian Brauner]

On Fri, Apr 10, 2026 at 04:09:18AM -0400, lirongqing wrote:
> 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>
> ---

That warning should very much serve as a reminder to not use that
completely unsafe pattern. So no, move to newer coredump infra or use
absolute paths, please.