When NETIF_F_HW_HSR_TAG_INS is enabled and frame->skb_std is NULL, hsr_create_tagged_frame() and prp_create_tagged_frame() call skb_clone() with a NULL pointer. Similarly, prp_get_untagged_frame() doesn't check if __pskb_copy() fails before calling skb_clone().
This causes a kernel crash reported by Syzbot:
Oops: general protection fault, probably for non-canonical address 0xdffffc000000000f: 0000 [#1] SMP KASAN NOPTI KASAN: null-ptr-deref in range [0x0000000000000078-0x000000000000007f] CPU: 0 UID: 0 PID: 5625 Comm: syz.1.18 Not tainted syzkaller #0 PREEMPT(full) Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014 RIP: 0010:skb_clone+0xd7/0x3a0 net/core/skbuff.c:2041 Code: 03 42 80 3c 20 00 74 08 4c 89 f7 e8 23 29 05 f9 49 83 3e 00 0f 85 a0 01 00 00 e8 94 dd 9d f8 48 8d 6b 7e 49 89 ee 49 c1 ee 03 <43> 0f b6 04 26 84 c0 0f 85 d1 01 00 00 44 0f b6 7d 00 41 83 e7 0c RSP: 0018:ffffc9000d00f200 EFLAGS: 00010207 RAX: ffffffff892235a1 RBX: 0000000000000000 RCX: ffff88803372a480 RDX: 0000000000000000 RSI: 0000000000000820 RDI: 0000000000000000 RBP: 000000000000007e R08: ffffffff8f7d0f77 R09: 1ffffffff1efa1ee R10: dffffc0000000000 R11: fffffbfff1efa1ef R12: dffffc0000000000 R13: 0000000000000820 R14: 000000000000000f R15: ffff88805144cc00 FS: 0000555557f6d500(0000) GS:ffff88808d72f000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000555581d35808 CR3: 000000005040e000 CR4: 0000000000352ef0 Call Trace: <TASK> hsr_forward_do net/hsr/hsr_forward.c:-1 [inline] hsr_forward_skb+0x1013/0x2860 net/hsr/hsr_forward.c:741 hsr_handle_frame+0x6ce/0xa70 net/hsr/hsr_slave.c:84 __netif_receive_skb_core+0x10b9/0x4380 net/core/dev.c:5966 __netif_receive_skb_one_core net/core/dev.c:6077 [inline] __netif_receive_skb+0x72/0x380 net/core/dev.c:6192 netif_receive_skb_internal net/core/dev.c:6278 [inline] netif_receive_skb+0x1cb/0x790 net/core/dev.c:6337 tun_rx_batched+0x1b9/0x730 drivers/net/tun.c:1485 tun_get_user+0x2b65/0x3e90 drivers/net/tun.c:1953 tun_chr_write_iter+0x113/0x200 drivers/net/tun.c:1999 new_sync_write fs/read_write.c:593 [inline] vfs_write+0x5c9/0xb30 fs/read_write.c:686 ksys_write+0x145/0x250 fs/read_write.c:738 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f0449f8e1ff Code: 89 54 24 18 48 89 74 24 10 89 7c 24 08 e8 f9 92 02 00 48 8b 54 24 18 48 8b 74 24 10 41 89 c0 8b 7c 24 08 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 31 44 89 c7 48 89 44 24 08 e8 4c 93 02 00 48 RSP: 002b:00007ffd7ad94c90 EFLAGS: 00000293 ORIG_RAX: 0000000000000001 RAX: ffffffffffffffda RBX: 00007f044a1e5fa0 RCX: 00007f0449f8e1ff RDX: 000000000000003e RSI: 0000200000000500 RDI: 00000000000000c8 RBP: 00007ffd7ad94d20 R08: 0000000000000000 R09: 0000000000000000 R10: 000000000000003e R11: 0000000000000293 R12: 0000000000000001 R13: 00007f044a1e5fa0 R14: 00007f044a1e5fa0 R15: 0000000000000003 </TASK>
Fix this by adding NULL checks for frame->skb_std before calling skb_clone() in the affected functions.
Reported-by: syzbot+2fa344348a579b779e05@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=2fa344348a579b779e05 Fixes: f266a683a480 ("net/hsr: Better frame dispatch") Cc: stable@vger.kernel.org Signed-off-by: Shaurya Rane ssrane_b23@ee.vjti.ac.in --- net/hsr/hsr_forward.c | 6 ++++++ 1 file changed, 6 insertions(+)
diff --git a/net/hsr/hsr_forward.c b/net/hsr/hsr_forward.c index 339f0d220212..8a8559f0880f 100644 --- a/net/hsr/hsr_forward.c +++ b/net/hsr/hsr_forward.c @@ -205,6 +205,8 @@ struct sk_buff *prp_get_untagged_frame(struct hsr_frame_info *frame, __pskb_copy(frame->skb_prp, skb_headroom(frame->skb_prp), GFP_ATOMIC); + if (!frame->skb_std) + return NULL; } else { /* Unexpected */ WARN_ONCE(1, "%s:%d: Unexpected frame received (port_src %s)\n", @@ -341,6 +343,8 @@ struct sk_buff *hsr_create_tagged_frame(struct hsr_frame_info *frame, hsr_set_path_id(frame, hsr_ethhdr, port); return skb_clone(frame->skb_hsr, GFP_ATOMIC); } else if (port->dev->features & NETIF_F_HW_HSR_TAG_INS) { + if (!frame->skb_std) + return NULL; return skb_clone(frame->skb_std, GFP_ATOMIC); }
@@ -385,6 +389,8 @@ struct sk_buff *prp_create_tagged_frame(struct hsr_frame_info *frame, } return skb_clone(frame->skb_prp, GFP_ATOMIC); } else if (port->dev->features & NETIF_F_HW_HSR_TAG_INS) { + if (!frame->skb_std) + return NULL; return skb_clone(frame->skb_std, GFP_ATOMIC); }
On Thu, Nov 27, 2025 at 10:02:19PM +0530, Shaurya Rane wrote:
When NETIF_F_HW_HSR_TAG_INS is enabled and frame->skb_std is NULL, hsr_create_tagged_frame() and prp_create_tagged_frame() call skb_clone() with a NULL pointer.
Have you acually tested this or do you have any other indication that this can happen? After all, you are suggesting that this kernel crash in a syzbot VM is caused by a (very uncommon) feature of hardware NICs.
Similarly, prp_get_untagged_frame() doesn't check if __pskb_copy() fails before calling skb_clone().
I suspect that this is really the only condition that can trigger the crash in question. This would also match that the syzbot reproducer hits this with a PRP interface (IFLA_HSR_PROTOCOL=0x1).
This causes a kernel crash reported by Syzbot:
Oops: general protection fault, probably for non-canonical address 0xdffffc000000000f: 0000 [#1] SMP KASAN NOPTI KASAN: null-ptr-deref in range [0x0000000000000078-0x000000000000007f] CPU: 0 UID: 0 PID: 5625 Comm: syz.1.18 Not tainted syzkaller #0 PREEMPT(full) Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014 RIP: 0010:skb_clone+0xd7/0x3a0 net/core/skbuff.c:2041 Code: 03 42 80 3c 20 00 74 08 4c 89 f7 e8 23 29 05 f9 49 83 3e 00 0f 85 a0 01 00 00 e8 94 dd 9d f8 48 8d 6b 7e 49 89 ee 49 c1 ee 03 <43> 0f b6 04 26 84 c0 0f 85 d1 01 00 00 44 0f b6 7d 00 41 83 e7 0c RSP: 0018:ffffc9000d00f200 EFLAGS: 00010207 RAX: ffffffff892235a1 RBX: 0000000000000000 RCX: ffff88803372a480 RDX: 0000000000000000 RSI: 0000000000000820 RDI: 0000000000000000 RBP: 000000000000007e R08: ffffffff8f7d0f77 R09: 1ffffffff1efa1ee R10: dffffc0000000000 R11: fffffbfff1efa1ef R12: dffffc0000000000 R13: 0000000000000820 R14: 000000000000000f R15: ffff88805144cc00 FS: 0000555557f6d500(0000) GS:ffff88808d72f000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000555581d35808 CR3: 000000005040e000 CR4: 0000000000352ef0 Call Trace:
<TASK> hsr_forward_do net/hsr/hsr_forward.c:-1 [inline] hsr_forward_skb+0x1013/0x2860 net/hsr/hsr_forward.c:741 hsr_handle_frame+0x6ce/0xa70 net/hsr/hsr_slave.c:84 __netif_receive_skb_core+0x10b9/0x4380 net/core/dev.c:5966 __netif_receive_skb_one_core net/core/dev.c:6077 [inline] __netif_receive_skb+0x72/0x380 net/core/dev.c:6192 netif_receive_skb_internal net/core/dev.c:6278 [inline] netif_receive_skb+0x1cb/0x790 net/core/dev.c:6337 tun_rx_batched+0x1b9/0x730 drivers/net/tun.c:1485 tun_get_user+0x2b65/0x3e90 drivers/net/tun.c:1953 tun_chr_write_iter+0x113/0x200 drivers/net/tun.c:1999 new_sync_write fs/read_write.c:593 [inline] vfs_write+0x5c9/0xb30 fs/read_write.c:686 ksys_write+0x145/0x250 fs/read_write.c:738 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f0449f8e1ff Code: 89 54 24 18 48 89 74 24 10 89 7c 24 08 e8 f9 92 02 00 48 8b 54 24 18 48 8b 74 24 10 41 89 c0 8b 7c 24 08 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 31 44 89 c7 48 89 44 24 08 e8 4c 93 02 00 48 RSP: 002b:00007ffd7ad94c90 EFLAGS: 00000293 ORIG_RAX: 0000000000000001 RAX: ffffffffffffffda RBX: 00007f044a1e5fa0 RCX: 00007f0449f8e1ff RDX: 000000000000003e RSI: 0000200000000500 RDI: 00000000000000c8 RBP: 00007ffd7ad94d20 R08: 0000000000000000 R09: 0000000000000000 R10: 000000000000003e R11: 0000000000000293 R12: 0000000000000001 R13: 00007f044a1e5fa0 R14: 00007f044a1e5fa0 R15: 0000000000000003 </TASK>
Fix this by adding NULL checks for frame->skb_std before calling skb_clone() in the affected functions.
Reported-by: syzbot+2fa344348a579b779e05@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=2fa344348a579b779e05 Fixes: f266a683a480 ("net/hsr: Better frame dispatch") Cc: stable@vger.kernel.org Signed-off-by: Shaurya Rane ssrane_b23@ee.vjti.ac.in
net/hsr/hsr_forward.c | 6 ++++++ 1 file changed, 6 insertions(+)
diff --git a/net/hsr/hsr_forward.c b/net/hsr/hsr_forward.c index 339f0d220212..8a8559f0880f 100644 --- a/net/hsr/hsr_forward.c +++ b/net/hsr/hsr_forward.c @@ -205,6 +205,8 @@ struct sk_buff *prp_get_untagged_frame(struct hsr_frame_info *frame, __pskb_copy(frame->skb_prp, skb_headroom(frame->skb_prp), GFP_ATOMIC);
if (!frame->skb_std)return NULL;
This check looks good to me.
@@ -341,6 +343,8 @@ struct sk_buff *hsr_create_tagged_frame(struct hsr_frame_info *frame, hsr_set_path_id(frame, hsr_ethhdr, port); return skb_clone(frame->skb_hsr, GFP_ATOMIC); } else if (port->dev->features & NETIF_F_HW_HSR_TAG_INS) {
if (!frame->skb_std)return NULL;@@ -385,6 +389,8 @@ struct sk_buff *prp_create_tagged_frame(struct hsr_frame_info *frame, } return skb_clone(frame->skb_prp, GFP_ATOMIC); } else if (port->dev->features & NETIF_F_HW_HSR_TAG_INS) {
if (!frame->skb_std)return NULL;
If any of these two conditions happen we have a different, serious problem that needs to be fixed elsewhere.
In hsr_create_tagged_frame(), we first check if we have an skb_hsr (an skb containing an already tagged message). If we don't, it has to be an skb_std (an skb without any tag). If !skb_std, we are either 1) handing around a frame without any skb; or 2) handing a PRP frame to an HSR function. In both cases, this would need to be fixed where the problem is introduced.
Thanks, Felix
On Fri, Nov 28, 2025 at 1:51 PM Felix Maurer fmaurer@redhat.com wrote:
On Thu, Nov 27, 2025 at 10:02:19PM +0530, Shaurya Rane wrote:
When NETIF_F_HW_HSR_TAG_INS is enabled and frame->skb_std is NULL, hsr_create_tagged_frame() and prp_create_tagged_frame() call skb_clone() with a NULL pointer.
Have you acually tested this or do you have any other indication that this can happen? After all, you are suggesting that this kernel crash in a syzbot VM is caused by a (very uncommon) feature of hardware NICs.
Agreed. The syzbot reproducer uses PRP (protocol=1), and the crash path goes through prp_get_untagged_frame() where __pskb_copy() can fail and return NULL. I tested the patch with syzbot and the bug no longer reproduces, confirming this is the actual root cause.
Similarly, prp_get_untagged_frame() doesn't check if __pskb_copy() fails before calling skb_clone().
I suspect that this is really the only condition that can trigger the crash in question. This would also match that the syzbot reproducer hits this with a PRP interface (IFLA_HSR_PROTOCOL=0x1).
That makes sense. I've dropped the NETIF_F_HW_HSR_TAG_INS checks and sent v3 with only the prp_get_untagged_frame() fix.That makes sense. I've dropped the NETIF_F_HW_HSR_TAG_INS checks and sent v3 with only the prp_get_untagged_frame() fix and tested it with the syzbot reproducer .
This causes a kernel crash reported by Syzbot:
Oops: general protection fault, probably for non-canonical address 0xdffffc000000000f: 0000 [#1] SMP KASAN NOPTI KASAN: null-ptr-deref in range [0x0000000000000078-0x000000000000007f] CPU: 0 UID: 0 PID: 5625 Comm: syz.1.18 Not tainted syzkaller #0 PREEMPT(full) Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014 RIP: 0010:skb_clone+0xd7/0x3a0 net/core/skbuff.c:2041 Code: 03 42 80 3c 20 00 74 08 4c 89 f7 e8 23 29 05 f9 49 83 3e 00 0f 85 a0 01 00 00 e8 94 dd 9d f8 48 8d 6b 7e 49 89 ee 49 c1 ee 03 <43> 0f b6 04 26 84 c0 0f 85 d1 01 00 00 44 0f b6 7d 00 41 83 e7 0c RSP: 0018:ffffc9000d00f200 EFLAGS: 00010207 RAX: ffffffff892235a1 RBX: 0000000000000000 RCX: ffff88803372a480 RDX: 0000000000000000 RSI: 0000000000000820 RDI: 0000000000000000 RBP: 000000000000007e R08: ffffffff8f7d0f77 R09: 1ffffffff1efa1ee R10: dffffc0000000000 R11: fffffbfff1efa1ef R12: dffffc0000000000 R13: 0000000000000820 R14: 000000000000000f R15: ffff88805144cc00 FS: 0000555557f6d500(0000) GS:ffff88808d72f000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000555581d35808 CR3: 000000005040e000 CR4: 0000000000352ef0 Call Trace:
<TASK> hsr_forward_do net/hsr/hsr_forward.c:-1 [inline] hsr_forward_skb+0x1013/0x2860 net/hsr/hsr_forward.c:741 hsr_handle_frame+0x6ce/0xa70 net/hsr/hsr_slave.c:84 __netif_receive_skb_core+0x10b9/0x4380 net/core/dev.c:5966 __netif_receive_skb_one_core net/core/dev.c:6077 [inline] __netif_receive_skb+0x72/0x380 net/core/dev.c:6192 netif_receive_skb_internal net/core/dev.c:6278 [inline] netif_receive_skb+0x1cb/0x790 net/core/dev.c:6337 tun_rx_batched+0x1b9/0x730 drivers/net/tun.c:1485 tun_get_user+0x2b65/0x3e90 drivers/net/tun.c:1953 tun_chr_write_iter+0x113/0x200 drivers/net/tun.c:1999 new_sync_write fs/read_write.c:593 [inline] vfs_write+0x5c9/0xb30 fs/read_write.c:686 ksys_write+0x145/0x250 fs/read_write.c:738 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f0449f8e1ff Code: 89 54 24 18 48 89 74 24 10 89 7c 24 08 e8 f9 92 02 00 48 8b 54 24 18 48 8b 74 24 10 41 89 c0 8b 7c 24 08 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 31 44 89 c7 48 89 44 24 08 e8 4c 93 02 00 48 RSP: 002b:00007ffd7ad94c90 EFLAGS: 00000293 ORIG_RAX: 0000000000000001 RAX: ffffffffffffffda RBX: 00007f044a1e5fa0 RCX: 00007f0449f8e1ff RDX: 000000000000003e RSI: 0000200000000500 RDI: 00000000000000c8 RBP: 00007ffd7ad94d20 R08: 0000000000000000 R09: 0000000000000000 R10: 000000000000003e R11: 0000000000000293 R12: 0000000000000001 R13: 00007f044a1e5fa0 R14: 00007f044a1e5fa0 R15: 0000000000000003 </TASK>
Fix this by adding NULL checks for frame->skb_std before calling skb_clone() in the affected functions.
Reported-by: syzbot+2fa344348a579b779e05@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=2fa344348a579b779e05 Fixes: f266a683a480 ("net/hsr: Better frame dispatch") Cc: stable@vger.kernel.org Signed-off-by: Shaurya Rane ssrane_b23@ee.vjti.ac.in
net/hsr/hsr_forward.c | 6 ++++++ 1 file changed, 6 insertions(+)
diff --git a/net/hsr/hsr_forward.c b/net/hsr/hsr_forward.c index 339f0d220212..8a8559f0880f 100644 --- a/net/hsr/hsr_forward.c +++ b/net/hsr/hsr_forward.c @@ -205,6 +205,8 @@ struct sk_buff *prp_get_untagged_frame(struct hsr_frame_info *frame, __pskb_copy(frame->skb_prp, skb_headroom(frame->skb_prp), GFP_ATOMIC);
if (!frame->skb_std)return NULL; } else { /* Unexpected */ WARN_ONCE(1, "%s:%d: Unexpected frame received (port_src %s)\n",This check looks good to me.
@@ -341,6 +343,8 @@ struct sk_buff *hsr_create_tagged_frame(struct hsr_frame_info *frame, hsr_set_path_id(frame, hsr_ethhdr, port); return skb_clone(frame->skb_hsr, GFP_ATOMIC); } else if (port->dev->features & NETIF_F_HW_HSR_TAG_INS) {
if (!frame->skb_std)return NULL; return skb_clone(frame->skb_std, GFP_ATOMIC); }@@ -385,6 +389,8 @@ struct sk_buff *prp_create_tagged_frame(struct hsr_frame_info *frame, } return skb_clone(frame->skb_prp, GFP_ATOMIC); } else if (port->dev->features & NETIF_F_HW_HSR_TAG_INS) {
if (!frame->skb_std)return NULL; return skb_clone(frame->skb_std, GFP_ATOMIC); }If any of these two conditions happen we have a different, serious problem that needs to be fixed elsewhere.
In hsr_create_tagged_frame(), we first check if we have an skb_hsr (an skb containing an already tagged message). If we don't, it has to be an skb_std (an skb without any tag). If !skb_std, we are either 1) handing around a frame without any skb; or 2) handing a PRP frame to an HSR function. In both cases, this would need to be fixed where the problem is introduced.
Thanks, Felix
Thanks, Shaurya
linux-stable-mirror@lists.linaro.org
-
Felix Maurer -
SHAURYA RANE -
Shaurya Rane