[PATCH net] net: ethernet: mtk_eth_soc: fix uninitialized variable

[PATCH net] net: ethernet: mtk_eth_soc: fix uninitialized variable

[Daniel Golle]

Variable dma_addr in function mtk_poll_rx can be uninitialized on
some of the error paths. In practise this doesn't matter, even random
data present in uninitialized stack memory can safely be used in the
way it happens in the error path.

However, in order to make Smatch happy make sure the variable is
always initialized.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
---
 drivers/net/ethernet/mediatek/mtk_eth_soc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.c b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
index 31090490d47ce..6342eac90793e 100644
--- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
+++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
@@ -2119,11 +2119,11 @@ static int mtk_poll_rx(struct napi_struct *napi, int budget,
 	u8 *data, *new_data;
 	struct mtk_rx_dma_v2 *rxd, trxd;
 	int done = 0, bytes = 0;
+	dma_addr_t dma_addr = NULL;
 
 	while (done < budget) {
 		unsigned int pktlen, *rxdcsum;
 		struct net_device *netdev;
-		dma_addr_t dma_addr;
 		u32 hash, reason;
 		int mac = 0;
 
-- 
2.42.0

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Re: [PATCH net] net: ethernet: mtk_eth_soc: fix uninitialized variable

[Simon Horman]

On Thu, Sep 07, 2023 at 04:14:20PM +0100, Daniel Golle wrote:
> Variable dma_addr in function mtk_poll_rx can be uninitialized on
> some of the error paths. In practise this doesn't matter, even random
> data present in uninitialized stack memory can safely be used in the
> way it happens in the error path.
> 
> However, in order to make Smatch happy make sure the variable is
> always initialized.
> 
> Signed-off-by: Daniel Golle <daniel@makrotopia.org>
> ---
>  drivers/net/ethernet/mediatek/mtk_eth_soc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.c b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
> index 31090490d47ce..6342eac90793e 100644
> --- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
> +++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
> @@ -2119,11 +2119,11 @@ static int mtk_poll_rx(struct napi_struct *napi, int budget,
>  	u8 *data, *new_data;
>  	struct mtk_rx_dma_v2 *rxd, trxd;
>  	int done = 0, bytes = 0;
> +	dma_addr_t dma_addr = NULL;

Hi Daniel,

I'm not sure that NULL is a valid value for a variable of type dma_addr_t.
Is DMA_MAPPING_ERROR more appropriate here?

Flagged by Sparse and, W=1 builds with gcc-13 and clang-16.

>  
>  	while (done < budget) {
>  		unsigned int pktlen, *rxdcsum;
>  		struct net_device *netdev;
> -		dma_addr_t dma_addr;
>  		u32 hash, reason;
>  		int mac = 0;
>  
> -- 
> 2.42.0
> 

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Re: [PATCH net] net: ethernet: mtk_eth_soc: fix uninitialized variable

[kernel test robot]

Hi Daniel,

kernel test robot noticed the following build warnings:

[auto build test WARNING on net/main]

url:    https://github.com/intel-lab-lkp/linux/commits/Daniel-Golle/net-ethernet-mtk_eth_soc-fix-uninitialized-variable/20230907-234141
base:   net/main
patch link:    https://lore.kernel.org/r/51d1ae238aecde07b2b4fe02cdab0dc87287cd96.1694099183.git.daniel%40makrotopia.org
patch subject: [PATCH net] net: ethernet: mtk_eth_soc: fix uninitialized variable
config: alpha-allyesconfig (https://download.01.org/0day-ci/archive/20230908/202309080027.e4rJ0o2x-lkp@intel.com/config)
compiler: alpha-linux-gcc (GCC) 13.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20230908/202309080027.e4rJ0o2x-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202309080027.e4rJ0o2x-lkp@intel.com/

All warnings (new ones prefixed by >>):

   In file included from include/uapi/linux/posix_types.h:5,
                    from include/uapi/linux/types.h:14,
                    from include/linux/types.h:6,
                    from include/linux/of.h:14,
                    from drivers/net/ethernet/mediatek/mtk_eth_soc.c:9:
   drivers/net/ethernet/mediatek/mtk_eth_soc.c: In function 'mtk_poll_rx':
>> include/linux/stddef.h:8:14: warning: initialization of 'dma_addr_t' {aka 'long long unsigned int'} from 'void *' makes integer from pointer without a cast [-Wint-conversion]
       8 | #define NULL ((void *)0)
         |              ^
   drivers/net/ethernet/mediatek/mtk_eth_soc.c:2008:31: note: in expansion of macro 'NULL'
    2008 |         dma_addr_t dma_addr = NULL;
         |                               ^~~~


vim +8 include/linux/stddef.h

^1da177e4c3f41 Linus Torvalds   2005-04-16  6  
^1da177e4c3f41 Linus Torvalds   2005-04-16  7  #undef NULL
^1da177e4c3f41 Linus Torvalds   2005-04-16 @8  #define NULL ((void *)0)
6e218287432472 Richard Knutsson 2006-09-30  9  

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Re: [PATCH net] net: ethernet: mtk_eth_soc: fix uninitialized variable

[kernel test robot]

Hi Daniel,

kernel test robot noticed the following build warnings:

[auto build test WARNING on net/main]

url:    https://github.com/intel-lab-lkp/linux/commits/Daniel-Golle/net-ethernet-mtk_eth_soc-fix-uninitialized-variable/20230907-234141
base:   net/main
patch link:    https://lore.kernel.org/r/51d1ae238aecde07b2b4fe02cdab0dc87287cd96.1694099183.git.daniel%40makrotopia.org
patch subject: [PATCH net] net: ethernet: mtk_eth_soc: fix uninitialized variable
config: parisc-allyesconfig (https://download.01.org/0day-ci/archive/20230908/202309080051.4UKDipfX-lkp@intel.com/config)
compiler: hppa-linux-gcc (GCC) 13.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20230908/202309080051.4UKDipfX-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202309080051.4UKDipfX-lkp@intel.com/

All warnings (new ones prefixed by >>):

   In file included from include/uapi/linux/posix_types.h:5,
                    from include/uapi/linux/types.h:14,
                    from include/linux/types.h:6,
                    from include/linux/of.h:14,
                    from drivers/net/ethernet/mediatek/mtk_eth_soc.c:9:
   drivers/net/ethernet/mediatek/mtk_eth_soc.c: In function 'mtk_poll_rx':
>> include/linux/stddef.h:8:14: warning: initialization of 'dma_addr_t' {aka 'unsigned int'} from 'void *' makes integer from pointer without a cast [-Wint-conversion]
       8 | #define NULL ((void *)0)
         |              ^
   drivers/net/ethernet/mediatek/mtk_eth_soc.c:2008:31: note: in expansion of macro 'NULL'
    2008 |         dma_addr_t dma_addr = NULL;
         |                               ^~~~


vim +8 include/linux/stddef.h

^1da177e4c3f41 Linus Torvalds   2005-04-16  6  
^1da177e4c3f41 Linus Torvalds   2005-04-16  7  #undef NULL
^1da177e4c3f41 Linus Torvalds   2005-04-16 @8  #define NULL ((void *)0)
6e218287432472 Richard Knutsson 2006-09-30  9  

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Re: [PATCH net] net: ethernet: mtk_eth_soc: fix uninitialized variable

[Dan Carpenter]

On Thu, Sep 07, 2023 at 04:14:20PM +0100, Daniel Golle wrote:
> Variable dma_addr in function mtk_poll_rx can be uninitialized on
> some of the error paths. In practise this doesn't matter, even random
> data present in uninitialized stack memory can safely be used in the
> way it happens in the error path.

KMemsan can detect unintialized memory at runtime as well.  But
presumably no one runs that on production systems.

regards,
dan carpenter


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[PATCH net v2] net: ethernet: mtk_eth_soc: fix uninitialized variable

[Daniel Golle]

Variable dma_addr in function mtk_poll_rx can be uninitialized on
some of the error paths. In practise this doesn't matter, even random
data present in uninitialized stack memory can safely be used in the
way it happens in the error path.

However, in order to make Smatch happy make sure the variable is
always initialized.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
---
v2: initialize with DMA_MAPPING_ERROR instead of NULL

 drivers/net/ethernet/mediatek/mtk_eth_soc.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.c b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
index 31090490d47ce..6145ddcff206c 100644
--- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
+++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
@@ -2119,11 +2119,11 @@ static int mtk_poll_rx(struct napi_struct *napi, int budget,
 	u8 *data, *new_data;
 	struct mtk_rx_dma_v2 *rxd, trxd;
 	int done = 0, bytes = 0;
+	dma_addr_t dma_addr = DMA_MAPPING_ERROR;
 
 	while (done < budget) {
 		unsigned int pktlen, *rxdcsum;
 		struct net_device *netdev;
-		dma_addr_t dma_addr;
 		u32 hash, reason;
 		int mac = 0;
 
@@ -2300,7 +2300,8 @@ static int mtk_poll_rx(struct napi_struct *napi, int budget,
 		else
 			rxd->rxd2 = RX_DMA_PREP_PLEN0(ring->buf_size);
 
-		if (MTK_HAS_CAPS(eth->soc->caps, MTK_36BIT_DMA))
+		if (MTK_HAS_CAPS(eth->soc->caps, MTK_36BIT_DMA) &&
+		    likely(dma_addr != DMA_MAPPING_ERROR))
 			rxd->rxd2 |= RX_DMA_PREP_ADDR64(dma_addr);
 
 		ring->calc_idx = idx;
-- 
2.42.0

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Re: [PATCH net v2] net: ethernet: mtk_eth_soc: fix uninitialized variable

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by David S. Miller <davem@davemloft.net>:

On Sun, 10 Sep 2023 22:40:30 +0100 you wrote:
> Variable dma_addr in function mtk_poll_rx can be uninitialized on
> some of the error paths. In practise this doesn't matter, even random
> data present in uninitialized stack memory can safely be used in the
> way it happens in the error path.
> 
> However, in order to make Smatch happy make sure the variable is
> always initialized.
> 
> [...]

Here is the summary with links:
  - [net,v2] net: ethernet: mtk_eth_soc: fix uninitialized variable
    https://git.kernel.org/netdev/net/c/e10a35abb3da

You are awesome, thank you!
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