[PATCH] net: atm: lec: add pre_send validation to avoid uninitialized

[PATCH] net: atm: lec: add pre_send validation to avoid uninitialized

[Dharanitharan R]

syzbot reported a KMSAN uninitialized-value crash caused by reading
fields from struct atmlec_msg before validating that the skb contains
enough linear data. A malformed short skb can cause lec_arp_update()
and other handlers to access uninitialized memory.

Add a pre_send() validator that ensures the message header and optional
TLVs are fully present. This prevents all lec message types from reading
beyond initialized skb data.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reported-by: syzbot+5dd615f890ddada54057@syzkaller.appspotmail.com
Tested-by: syzbot+5dd615f890ddada54057@syzkaller.appspotmail.com

Closes: https://syzkaller.appspot.com/bug?extid=5dd615f890ddada54057

Signed-off-by: Dharanitharan R <dharanitharan725@gmail.com>
---
 net/atm/lec.c | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/net/atm/lec.c b/net/atm/lec.c
index afb8d3eb2185..c893781a490a 100644
--- a/net/atm/lec.c
+++ b/net/atm/lec.c
@@ -489,8 +489,33 @@ static void lec_atm_close(struct atm_vcc *vcc)
 	module_put(THIS_MODULE);
 }
 
+static int lec_atm_pre_send(struct atm_vcc *vcc, struct sk_buff *skb)
+{
+	struct atmlec_msg *mesg;
+	u32 sizeoftlvs;
+	unsigned int msg_size = sizeof(struct atmlec_msg);
+
+	/* Must contain the base message */
+	if (skb->len < msg_size)
+		return -EINVAL;
+
+   /* Must have at least msg_size bytes in linear data */
+   if (!pskb_may_pull(skb, msg_size))
+   	return -EINVAL;
+
+	mesg = (struct atmlec_msg *)skb->data;
+   sizeoftlvs = mesg->sizeoftlvs;
+
+   /* Validate TLVs if present */
+   if (sizeoftlvs && !pskb_may_pull(skb, msg_size + sizeoftlvs))
+       return -EINVAL;
+
+   return 0;
+}
+
 static const struct atmdev_ops lecdev_ops = {
 	.close = lec_atm_close,
+	.pre_send = lec_atm_pre_send, 
 	.send = lec_atm_send
 };
 
-- 
2.43.0

Re: [PATCH] net: atm: lec: add pre_send validation to avoid uninitialized

[kernel test robot]

Hi Dharanitharan,

kernel test robot noticed the following build warnings:

[auto build test WARNING on net/main]
[also build test WARNING on net-next/main linus/master horms-ipvs/master v6.18 next-20251205]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Dharanitharan-R/net-atm-lec-add-pre_send-validation-to-avoid-uninitialized/20251207-121647
base:   net/main
patch link:    https://lore.kernel.org/r/20251207041453.8302-1-dharanitharan725%40gmail.com
patch subject: [PATCH] net: atm: lec: add pre_send validation to avoid uninitialized
config: nios2-randconfig-002-20251208 (https://download.01.org/0day-ci/archive/20251208/202512080911.BLjFHfAd-lkp@intel.com/config)
compiler: nios2-linux-gcc (GCC) 11.5.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20251208/202512080911.BLjFHfAd-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/202512080911.BLjFHfAd-lkp@intel.com/

All warnings (new ones prefixed by >>):

   net/atm/lec.c: In function 'lec_atm_pre_send':
>> net/atm/lec.c:503:4: warning: this 'if' clause does not guard... [-Wmisleading-indentation]
     503 |    if (!pskb_may_pull(skb, msg_size))
         |    ^~
   net/atm/lec.c:506:9: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'if'
     506 |         mesg = (struct atmlec_msg *)skb->data;
         |         ^~~~

Kconfig warnings: (for reference only)
   WARNING: unmet direct dependencies detected for CAN_DEV
   Depends on [n]: NETDEVICES [=n] && CAN [=m]
   Selected by [m]:
   - CAN [=m] && NET [=y]


vim +/if +503 net/atm/lec.c

   491	
   492	static int lec_atm_pre_send(struct atm_vcc *vcc, struct sk_buff *skb)
   493	{
   494		struct atmlec_msg *mesg;
   495		u32 sizeoftlvs;
   496		unsigned int msg_size = sizeof(struct atmlec_msg);
   497	
   498		/* Must contain the base message */
   499		if (skb->len < msg_size)
   500			return -EINVAL;
   501	
   502	   /* Must have at least msg_size bytes in linear data */
 > 503	   if (!pskb_may_pull(skb, msg_size))
   504	   	return -EINVAL;
   505	
   506		mesg = (struct atmlec_msg *)skb->data;
   507	   sizeoftlvs = mesg->sizeoftlvs;
   508	
   509	   /* Validate TLVs if present */
   510	   if (sizeoftlvs && !pskb_may_pull(skb, msg_size + sizeoftlvs))
   511	       return -EINVAL;
   512	
   513	   return 0;
   514	}
   515	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH] net: atm: lec: add pre_send validation to avoid uninitialized

[kernel test robot]

Hi Dharanitharan,

kernel test robot noticed the following build warnings:

[auto build test WARNING on net/main]
[also build test WARNING on net-next/main linus/master horms-ipvs/master v6.18 next-20251205]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Dharanitharan-R/net-atm-lec-add-pre_send-validation-to-avoid-uninitialized/20251207-121647
base:   net/main
patch link:    https://lore.kernel.org/r/20251207041453.8302-1-dharanitharan725%40gmail.com
patch subject: [PATCH] net: atm: lec: add pre_send validation to avoid uninitialized
config: arm64-randconfig-002-20251208 (https://download.01.org/0day-ci/archive/20251208/202512081042.Zx4NasDJ-lkp@intel.com/config)
compiler: clang version 18.1.8 (https://github.com/llvm/llvm-project 3b5b5c1ec4a3095ab096dd780e84d7ab81f3d7ff)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20251208/202512081042.Zx4NasDJ-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/202512081042.Zx4NasDJ-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> net/atm/lec.c:506:2: warning: misleading indentation; statement is not part of the previous 'if' [-Wmisleading-indentation]
     506 |         mesg = (struct atmlec_msg *)skb->data;
         |         ^
   net/atm/lec.c:503:4: note: previous statement is here
     503 |    if (!pskb_may_pull(skb, msg_size))
         |    ^
   1 warning generated.


vim +/if +506 net/atm/lec.c

   491	
   492	static int lec_atm_pre_send(struct atm_vcc *vcc, struct sk_buff *skb)
   493	{
   494		struct atmlec_msg *mesg;
   495		u32 sizeoftlvs;
   496		unsigned int msg_size = sizeof(struct atmlec_msg);
   497	
   498		/* Must contain the base message */
   499		if (skb->len < msg_size)
   500			return -EINVAL;
   501	
   502	   /* Must have at least msg_size bytes in linear data */
   503	   if (!pskb_may_pull(skb, msg_size))
   504	   	return -EINVAL;
   505	
 > 506		mesg = (struct atmlec_msg *)skb->data;
   507	   sizeoftlvs = mesg->sizeoftlvs;
   508	
   509	   /* Validate TLVs if present */
   510	   if (sizeoftlvs && !pskb_may_pull(skb, msg_size + sizeoftlvs))
   511	       return -EINVAL;
   512	
   513	   return 0;
   514	}
   515	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH] net: atm: lec: add pre_send validation to avoid uninitialized

[Simon Horman]

+ Edward

On Sun, Dec 07, 2025 at 04:14:53AM +0000, Dharanitharan R wrote:
> syzbot reported a KMSAN uninitialized-value crash caused by reading
> fields from struct atmlec_msg before validating that the skb contains
> enough linear data. A malformed short skb can cause lec_arp_update()
> and other handlers to access uninitialized memory.
> 
> Add a pre_send() validator that ensures the message header and optional
> TLVs are fully present. This prevents all lec message types from reading
> beyond initialized skb data.
> 
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Reported-by: syzbot+5dd615f890ddada54057@syzkaller.appspotmail.com
> Tested-by: syzbot+5dd615f890ddada54057@syzkaller.appspotmail.com

No blank lines between tags please.

> 
> Closes: https://syzkaller.appspot.com/bug?extid=5dd615f890ddada54057

Likewise here.

> 
> Signed-off-by: Dharanitharan R <dharanitharan725@gmail.com>

But more importantly, this seems to duplicate another patch
that is under review:

* [PATCH net v3] net: atm: implement pre_send to check input before sending
  https://lore.kernel.org/all/tencent_4312C2065549BCEEF0EECACCA467F446F406@qq.com/

Re: [PATCH] net: atm: lec: add pre_send validation to avoid uninitialized

[kernel test robot]

Hi Dharanitharan,

kernel test robot noticed the following build warnings:

[auto build test WARNING on net/main]
[also build test WARNING on net-next/main linus/master v6.18 next-20251208]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Dharanitharan-R/net-atm-lec-add-pre_send-validation-to-avoid-uninitialized/20251207-121647
base:   net/main
patch link:    https://lore.kernel.org/r/20251207041453.8302-1-dharanitharan725%40gmail.com
patch subject: [PATCH] net: atm: lec: add pre_send validation to avoid uninitialized
config: x86_64-randconfig-r072-20251208 (https://download.01.org/0day-ci/archive/20251209/202512090202.P59kzmhm-lkp@intel.com/config)
compiler: gcc-14 (Debian 14.2.0-19) 14.2.0

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/202512090202.P59kzmhm-lkp@intel.com/

New smatch warnings:
net/atm/lec.c:503 lec_atm_pre_send() warn: inconsistent indenting
net/atm/lec.c:506 lec_atm_pre_send() warn: curly braces intended?

Old smatch warnings:
net/atm/lec.c:507 lec_atm_pre_send() warn: inconsistent indenting

vim +503 net/atm/lec.c

   491	
   492	static int lec_atm_pre_send(struct atm_vcc *vcc, struct sk_buff *skb)
   493	{
   494		struct atmlec_msg *mesg;
   495		u32 sizeoftlvs;
   496		unsigned int msg_size = sizeof(struct atmlec_msg);
   497	
   498		/* Must contain the base message */
   499		if (skb->len < msg_size)
   500			return -EINVAL;
   501	
   502	   /* Must have at least msg_size bytes in linear data */
 > 503	   if (!pskb_may_pull(skb, msg_size))
   504	   	return -EINVAL;
   505	
 > 506		mesg = (struct atmlec_msg *)skb->data;
   507	   sizeoftlvs = mesg->sizeoftlvs;
   508	
   509	   /* Validate TLVs if present */
   510	   if (sizeoftlvs && !pskb_may_pull(skb, msg_size + sizeoftlvs))
   511	       return -EINVAL;
   512	
   513	   return 0;
   514	}
   515	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki