linux-kernel - Re: [PATCH v4] cxl: Fix possible null pointer dereference in read

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Message-ID: <87y163w4n4.fsf@mail.lhotse>
Date: Mon, 15 Jul 2024 16:28:15 +1000
From: Michael Ellerman <mpe@...erman.id.au>
To: Ma Ke <make24@...as.ac.cn>, fbarrat@...ux.ibm.com, ajd@...ux.ibm.com,
 arnd@...db.de, gregkh@...uxfoundation.org, manoj@...ux.vnet.ibm.com,
 imunsie@....ibm.com, clombard@...ux.vnet.ibm.com
Cc: linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org, Ma Ke
 <make24@...as.ac.cn>, stable@...r.kernel.org
Subject: Re: [PATCH v4] cxl: Fix possible null pointer dereference in
 read_handle()

Ma Ke <make24@...as.ac.cn> writes:
> In read_handle(), of_get_address() may return NULL if getting address and
> size of the node failed. When of_read_number() uses prop to handle
> conversions between different byte orders, it could lead to a null pointer
> dereference. Add NULL check to fix potential issue.
>
> Found by static analysis.
>
> Cc: stable@...r.kernel.org
> Fixes: 14baf4d9c739 ("cxl: Add guest-specific code")
> Signed-off-by: Ma Ke <make24@...as.ac.cn>
> ---
> Changes in v4:
> - modified vulnerability description according to suggestions, making the 
> process of static analysis of vulnerabilities clearer. No active research 
> on developer behavior.
> Changes in v3:
> - fixed up the changelog text as suggestions.
> Changes in v2:
> - added an explanation of how the potential vulnerability was discovered,
> but not meet the description specification requirements.
> ---
>  drivers/misc/cxl/of.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/misc/cxl/of.c b/drivers/misc/cxl/of.c
> index bcc005dff1c0..d8dbb3723951 100644
> --- a/drivers/misc/cxl/of.c
> +++ b/drivers/misc/cxl/of.c
> @@ -58,7 +58,7 @@ static int read_handle(struct device_node *np, u64 *handle)
>  
>  	/* Get address and size of the node */
>  	prop = of_get_address(np, 0, &size, NULL);
> -	if (size)
> +	if (!prop || size)
>  		return -EINVAL;
>  
>  	/* Helper to read a big number; size is in cells (not bytes) */

If you expand the context this could just use of_property_read_reg(),
something like below.

cheers


diff --git a/drivers/misc/cxl/of.c b/drivers/misc/cxl/of.c
index bcc005dff1c0..a184855b2a7b 100644
--- a/drivers/misc/cxl/of.c
+++ b/drivers/misc/cxl/of.c
@@ -53,16 +53,15 @@ static const __be64 *read_prop64_dword(const struct device_node *np,
 
 static int read_handle(struct device_node *np, u64 *handle)
 {
-	const __be32 *prop;
 	u64 size;
+	
+	if (of_property_read_reg(np, 0, handle, &size))
+		return -EINVAL;
 
-	/* Get address and size of the node */
-	prop = of_get_address(np, 0, &size, NULL);
+	// Size must be zero per PAPR+ v2.13 § C.6.19
 	if (size)
 		return -EINVAL;
 
-	/* Helper to read a big number; size is in cells (not bytes) */
-	*handle = of_read_number(prop, of_n_addr_cells(np));
 	return 0;
 }