[PATCH] lib/vsprintf: Require exact hash_pointers mode matches

[PATCH] lib/vsprintf: Require exact hash_pointers mode matches

[Kaitao Cheng]

From: Kaitao Cheng <chengkaitao@kylinos.cn>

hash_pointers= accepts a small set of mode strings, but the parser uses
strncmp() with the length of each valid mode.  That accepts values with
trailing garbage, such as hash_pointers=autobots or
hash_pointers=nevermind, as valid aliases for auto and never.

Use strcmp() so that only the documented mode strings are accepted.
Invalid values will continue to fall back to auto through the existing
unknown-mode path.

Signed-off-by: Kaitao Cheng <chengkaitao@kylinos.cn>
---
 lib/vsprintf.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 9ca676feb8eb..03e87b933fd0 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -2354,13 +2354,13 @@ static int __init hash_pointers_mode_parse(char *str)
 	if (!str) {
 		pr_warn("Hash pointers mode empty; falling back to auto.\n");
 		hash_pointers_mode = HASH_PTR_AUTO;
-	} else if (strncmp(str, "auto", 4) == 0)   {
+	} else if (strcmp(str, "auto") == 0) {
 		pr_info("Hash pointers mode set to auto.\n");
 		hash_pointers_mode = HASH_PTR_AUTO;
-	} else if (strncmp(str, "never", 5) == 0) {
+	} else if (strcmp(str, "never") == 0) {
 		pr_info("Hash pointers mode set to never.\n");
 		hash_pointers_mode = HASH_PTR_NEVER;
-	} else if (strncmp(str, "always", 6) == 0) {
+	} else if (strcmp(str, "always") == 0) {
 		pr_info("Hash pointers mode set to always.\n");
 		hash_pointers_mode = HASH_PTR_ALWAYS;
 	} else {
-- 
2.50.1 (Apple Git-155)

Re: [PATCH] lib/vsprintf: Require exact hash_pointers mode matches

[Petr Mladek]

On Tue 2026-05-19 21:01:17, Kaitao Cheng wrote:
> From: Kaitao Cheng <chengkaitao@kylinos.cn>
> 
> hash_pointers= accepts a small set of mode strings, but the parser uses
> strncmp() with the length of each valid mode.  That accepts values with
> trailing garbage, such as hash_pointers=autobots or
> hash_pointers=nevermind, as valid aliases for auto and never.
> 
> Use strcmp() so that only the documented mode strings are accepted.
> Invalid values will continue to fall back to auto through the existing
> unknown-mode path.
> 
> Signed-off-by: Kaitao Cheng <chengkaitao@kylinos.cn>

LGTM:

Reviewed-by: Petr Mladek <pmladek@suse.com>

I am going to queue this patch via the printk tree early next
week unless anyone complains in the meantime.

Best Regards,
Petr

Re: [PATCH] lib/vsprintf: Require exact hash_pointers mode matches

[Petr Mladek]

On Tue 2026-05-19 21:01:17, Kaitao Cheng wrote:
> From: Kaitao Cheng <chengkaitao@kylinos.cn>
> 
> hash_pointers= accepts a small set of mode strings, but the parser uses
> strncmp() with the length of each valid mode.  That accepts values with
> trailing garbage, such as hash_pointers=autobots or
> hash_pointers=nevermind, as valid aliases for auto and never.
> 
> Use strcmp() so that only the documented mode strings are accepted.
> Invalid values will continue to fall back to auto through the existing
> unknown-mode path.
> 
> Signed-off-by: Kaitao Cheng <chengkaitao@kylinos.cn>

JFYI, the patch has been committed into printk/linux.git,
branch for-7.2.

Best Regards,
Petr