2023-12-17 09:32:13

by Christophe JAILLET

Subject: [PATCH] x86/callthunks: Fix some potential string truncation in callthunks_debugfs_init()

When compiled with W=1, we get:
arch/x86/kernel/callthunks.c: In function ‘callthunks_debugfs_init’:
arch/x86/kernel/callthunks.c:394:35: error: ‘%lu’ directive writing between 1 and 10 bytes into a region of size 7 [-Werror=format-overflow=]
394 | sprintf(name, "cpu%lu", cpu);
| ^~~
arch/x86/kernel/callthunks.c:394:31: note: directive argument in the range [0, 4294967294]
394 | sprintf(name, "cpu%lu", cpu);
| ^~~~~~~~
arch/x86/kernel/callthunks.c:394:17: note: ‘sprintf’ output between 5 and 14 bytes into a destination of size 10
394 | sprintf(name, "cpu%lu", cpu);
|

So, give some more space to 'name' to silence the warning. (and fix the
issue should a lucky one have a config with so many CPU!)

Signed-off-by: Christophe JAILLET <[email protected]>
---
arch/x86/kernel/callthunks.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/callthunks.c b/arch/x86/kernel/callthunks.c
index cf7e5be1b844..26182a7d12b3 100644
--- a/arch/x86/kernel/callthunks.c
+++ b/arch/x86/kernel/callthunks.c
@@ -388,7 +388,7 @@ static int __init callthunks_debugfs_init(void)
dir = debugfs_create_dir("callthunks", NULL);
for_each_possible_cpu(cpu) {
void *arg = (void *)cpu;
- char name [10];
+ char name[14];

sprintf(name, "cpu%lu", cpu);
debugfs_create_file(name, 0644, dir, arg, &dfs_ops);
--
2.34.1

2023-12-19 11:03:39

by Sohil Mehta

Subject: Re: [PATCH] x86/callthunks: Fix some potential string truncation in callthunks_debugfs_init()

On 12/17/2023 2:31 PM, Christophe JAILLET wrote:
> When compiled with W=1, we get:
> arch/x86/kernel/callthunks.c: In function ‘callthunks_debugfs_init’:
> arch/x86/kernel/callthunks.c:394:35: error: ‘%lu’ directive writing between 1 and 10 bytes into a region of size 7 [-Werror=format-overflow=]
> 394 | sprintf(name, "cpu%lu", cpu);
> | ^~~
> arch/x86/kernel/callthunks.c:394:31: note: directive argument in the range [0, 4294967294]
> 394 | sprintf(name, "cpu%lu", cpu);
> | ^~~~~~~~
> arch/x86/kernel/callthunks.c:394:17: note: ‘sprintf’ output between 5 and 14 bytes into a destination of size 10
> 394 | sprintf(name, "cpu%lu", cpu);
> |
>
> So, give some more space to 'name' to silence the warning.

It might be useful to specify that "some more space" hasn't been
arbitrarily decided. It took me a few minutes to figure that out.

With the max cpu number being 4294967294 with 10 characters, a total of
14 chars would be enough to print "cpu%lu".


> (and fix the issue should a lucky one have a config with so many
> CPU!)
> Signed-off-by: Christophe JAILLET <[email protected]>
> ---
> arch/x86/kernel/callthunks.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>

Apart from that, please feel free to add:

Reviewed-by: Sohil Mehta <[email protected]>

> diff --git a/arch/x86/kernel/callthunks.c b/arch/x86/kernel/callthunks.c
> index cf7e5be1b844..26182a7d12b3 100644
> --- a/arch/x86/kernel/callthunks.c
> +++ b/arch/x86/kernel/callthunks.c
> @@ -388,7 +388,7 @@ static int __init callthunks_debugfs_init(void)
> dir = debugfs_create_dir("callthunks", NULL);
> for_each_possible_cpu(cpu) {
> void *arg = (void *)cpu;
> - char name [10];
> + char name[14];
>
> sprintf(name, "cpu%lu", cpu);
> debugfs_create_file(name, 0644, dir, arg, &dfs_ops);

2023-12-19 18:08:28

by Christophe JAILLET

Subject: Re: [PATCH] x86/callthunks: Fix some potential string truncation in callthunks_debugfs_init()

Le 19/12/2023 à 12:02, Sohil Mehta a écrit :
> On 12/17/2023 2:31 PM, Christophe JAILLET wrote:
>> When compiled with W=1, we get:
>> arch/x86/kernel/callthunks.c: In function ‘callthunks_debugfs_init’:
>> arch/x86/kernel/callthunks.c:394:35: error: ‘%lu’ directive writing between 1 and 10 bytes into a region of size 7 [-Werror=format-overflow=]
>> 394 | sprintf(name, "cpu%lu", cpu);
>> | ^~~
>> arch/x86/kernel/callthunks.c:394:31: note: directive argument in the range [0, 4294967294]
>> 394 | sprintf(name, "cpu%lu", cpu);
>> | ^~~~~~~~
>> arch/x86/kernel/callthunks.c:394:17: note: ‘sprintf’ output between 5 and 14 bytes into a destination of size 10
>> 394 | sprintf(name, "cpu%lu", cpu);
>> |
>>
>> So, give some more space to 'name' to silence the warning.
>
> It might be useful to specify that "some more space" hasn't been
> arbitrarily decided. It took me a few minutes to figure that out.
>
> With the max cpu number being 4294967294 with 10 characters, a total of
> 14 chars would be enough to print "cpu%lu".

From my POV, it is what the gcc warning already says, but I (or anyone
else) can tweak the wording to make it more explicit.

Let me know if you want a v2.

CJ

>
>
>> (and fix the issue should a lucky one have a config with so many
>> CPU!)
>> Signed-off-by: Christophe JAILLET <[email protected]>
>> ---
>> arch/x86/kernel/callthunks.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>
> Apart from that, please feel free to add:
>
> Reviewed-by: Sohil Mehta <[email protected]>
>
>> diff --git a/arch/x86/kernel/callthunks.c b/arch/x86/kernel/callthunks.c
>> index cf7e5be1b844..26182a7d12b3 100644
>> --- a/arch/x86/kernel/callthunks.c
>> +++ b/arch/x86/kernel/callthunks.c
>> @@ -388,7 +388,7 @@ static int __init callthunks_debugfs_init(void)
>> dir = debugfs_create_dir("callthunks", NULL);
>> for_each_possible_cpu(cpu) {
>> void *arg = (void *)cpu;
>> - char name [10];
>> + char name[14];
>>
>> sprintf(name, "cpu%lu", cpu);
>> debugfs_create_file(name, 0644, dir, arg, &dfs_ops);
>
>
>