ACK: Re: [SRU][J][PATCH 0/1] CVE-2025-21855

[Paolo Pisati]

On Thu, Oct 23, 2025 at 02:24:42PM +0200, Alessio Faina wrote:
> https://ubuntu.com/security/CVE-2025-21855
> 
> [ Impact ]
> 
> ibmvnic: Don't reference skb after sending to VIOS
> Previously, after successfully flushing the xmit buffer to VIOS,
> the tx_bytes stat was incremented by the length of the skb.
> 
> It is invalid to access the skb memory after sending the buffer to
> the VIOS because, at any point after sending, the VIOS can trigger
> an interrupt to free this memory. A race between reading skb->len
> and freeing the skb is possible (especially during LPM) and will
> result in use-after-free:
>  ==================================================================
>  BUG: KASAN: slab-use-after-free in ibmvnic_xmit+0x75c/0x1808 [ibmvnic]
>  Read of size 4 at addr c00000024eb48a70 by task hxecom/14495
>  <...>
>  Call Trace:
>  [c000000118f66cf0] [c0000000018cba6c] dump_stack_lvl+0x84/0xe8 (unreliable)
>  [c000000118f66d20] [c0000000006f0080] print_report+0x1a8/0x7f0
>  [c000000118f66df0] [c0000000006f08f0] kasan_report+0x128/0x1f8
>  [c000000118f66f00] [c0000000006f2868] __asan_load4+0xac/0xe0
>  [c000000118f66f20] [c0080000046eac84] ibmvnic_xmit+0x75c/0x1808 [ibmvnic]
>  [c000000118f67340] [c0000000014be168] dev_hard_start_xmit+0x150/0x358
>  <...>
>  Freed by task 0:
>  kasan_save_stack+0x34/0x68
>  kasan_save_track+0x2c/0x50
>  kasan_save_free_info+0x64/0x108
>  __kasan_mempool_poison_object+0x148/0x2d4
>  napi_skb_cache_put+0x5c/0x194
>  net_tx_action+0x154/0x5b8
>  handle_softirqs+0x20c/0x60c
>  do_softirq_own_stack+0x6c/0x88
>  <...>
>  The buggy address belongs to the object at c00000024eb48a00 which
>   belongs to the cache skbuff_head_cache of size 224
> ==================================================================
> 
> Fixes: 032c5e82847a ("Driver for IBM System i/p VNIC protocol")
> Signed-off-by: Nick Child <nnac123 at linux.ibm.com>
> Reviewed-by: Simon Horman <horms at kernel.org>
> Link: https://patch.msgid.link/20250214155233.235559-1-nnac123@linux.ibm.com
> Signed-off-by: Jakub Kicinski <kuba at kernel.org>
> 
> [ Fix ]
> 
> Backport commit bdf5d13aa05e from upstream
> 
> Questing: not affected
> Plucky:   not affected
> Noble:    not affected
> Jammy:    backported from upstream
> Focal:    fixed separately
> Bionic:   fixed separately
> Xenial:   fixed separately
> Trusty:   not affected
> 
> [ Test plan ]
> 
> Compiled and boot tested
> 
> [ Regression potential ]
> 
> Small code fix, and can only affect using a IBM virtual NIC device,
> low regression potential
> 
> Nick Child (1):
>   ibmvnic: Don't reference skb after sending to VIOS
> 
>  drivers/net/ethernet/ibm/ibmvnic.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> -- 
> 2.43.0
> 
> 
> -- 
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> kernel-team at lists.ubuntu.com
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Acked-by: Paolo Pisati <paolo.pisati at canonical.com>
-- 
bye,
p.