[PATCH] mm: cma: fix stack corruption due to sprintf usage

[PATCH] mm: cma: fix stack corruption due to sprintf usage

[Prakash Gupta]

name[] in cma_debugfs_add_one() can only accommodate 16 chars including
NULL to store sprintf output.  It's common for cma device name to be larger
than 15 chars. This can cause stack corrpution. If the gcc stack protector
is turned on, this can cause a panic due to stack corruption.

Below is one example trace:

Kernel panic - not syncing: stack-protector: Kernel stack is corrupted in:
ffffff8e69a75730
Call trace:
  [<ffffff8e68289504>] dump_backtrace+0x0/0x2c4
  [<ffffff8e682897e8>] show_stack+0x20/0x28
  [<ffffff8e685ea808>] dump_stack+0xb8/0xf4
  [<ffffff8e683c454c>] panic+0x154/0x2b0
  [<ffffff8e682a724c>] print_tainted+0x0/0xc0
  [<ffffff8e69a75730>] cma_debugfs_init+0x274/0x290
  [<ffffff8e682839ec>] do_one_initcall+0x5c/0x168
  [<ffffff8e69a50e24>] kernel_init_freeable+0x1c8/0x280

Fix the short sprintf buffer in cma_debugfs_add_one() by using scnprintf()
instead of sprintf().

fixes: f318dd083c81 ("cma: Store a name in the cma structure")
Signed-off-by: Prakash Gupta <guptap@codeaurora.org>
---
 mm/cma_debug.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/cma_debug.c b/mm/cma_debug.c
index 595b757..c03ccbc 100644
--- a/mm/cma_debug.c
+++ b/mm/cma_debug.c
@@ -167,7 +167,7 @@ static void cma_debugfs_add_one(struct cma *cma, int idx)
 	char name[16];
 	int u32s;
 
-	sprintf(name, "cma-%s", cma->name);
+	scnprintf(name, sizeof(name), "cma-%s", cma->name);
 
 	tmp = debugfs_create_dir(name, cma_debugfs_root);
 
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Re: [PATCH] mm: cma: fix stack corruption due to sprintf usage

[Laura Abbott]

On 08/11/2017 03:10 AM, Prakash Gupta wrote:
> name[] in cma_debugfs_add_one() can only accommodate 16 chars including
> NULL to store sprintf output.  It's common for cma device name to be larger
> than 15 chars. This can cause stack corrpution. If the gcc stack protector
> is turned on, this can cause a panic due to stack corruption.
> 
> Below is one example trace:
> 
> Kernel panic - not syncing: stack-protector: Kernel stack is corrupted in:
> ffffff8e69a75730
> Call trace:
>   [<ffffff8e68289504>] dump_backtrace+0x0/0x2c4
>   [<ffffff8e682897e8>] show_stack+0x20/0x28
>   [<ffffff8e685ea808>] dump_stack+0xb8/0xf4
>   [<ffffff8e683c454c>] panic+0x154/0x2b0
>   [<ffffff8e682a724c>] print_tainted+0x0/0xc0
>   [<ffffff8e69a75730>] cma_debugfs_init+0x274/0x290
>   [<ffffff8e682839ec>] do_one_initcall+0x5c/0x168
>   [<ffffff8e69a50e24>] kernel_init_freeable+0x1c8/0x280
> 
> Fix the short sprintf buffer in cma_debugfs_add_one() by using scnprintf()
> instead of sprintf().
> 

Acked-by: Laura Abbott <labbott@redhat.com>

> fixes: f318dd083c81 ("cma: Store a name in the cma structure")
> Signed-off-by: Prakash Gupta <guptap@codeaurora.org>
> ---
>  mm/cma_debug.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/cma_debug.c b/mm/cma_debug.c
> index 595b757..c03ccbc 100644
> --- a/mm/cma_debug.c
> +++ b/mm/cma_debug.c
> @@ -167,7 +167,7 @@ static void cma_debugfs_add_one(struct cma *cma, int idx)
>  	char name[16];
>  	int u32s;
>  
> -	sprintf(name, "cma-%s", cma->name);
> +	scnprintf(name, sizeof(name), "cma-%s", cma->name);
>  
>  	tmp = debugfs_create_dir(name, cma_debugfs_root);
>  
> 

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