ACK: [SRU][M][PATCH 0/1] CVE-2024-26805

Stefan Bader stefan.bader at canonical.com
Wed Apr 24 14:39:27 UTC 2024 

On 23.04.24 18:37, Bethany Jamison wrote:
> [Impact]
> 
>   In the Linux kernel, the following vulnerability has been resolved:
> 
>   netlink: Fix kernel-infoleak-after-free in __skb_datagram_iter
> 
>   syzbot reported the following uninit-value access issue [1]:
> 
>   netlink_to_full_skb() creates a new `skb` and puts the `skb->data`
>   passed as a 1st arg of netlink_to_full_skb() onto new `skb`. The data
>   size is specified as `len` and passed to skb_put_data(). This `len`
>   is based on `skb->end` that is not data offset but buffer offset. The
>   `skb->end` contains data and tailroom. Since the tailroom is not
>   initialized when the new `skb` created, KMSAN detects uninitialized
>   memory area when copying the data.
> 
>   This patch resolved this issue by correct the len from `skb->end` to
>   `skb->len`, which is the actual data offset.
> 
>   BUG: KMSAN: kernel-infoleak-after-free in instrument_copy_to_user
>   include/linux/instrumented.h:114 [inline]
>   BUG: KMSAN: kernel-infoleak-after-free in copy_to_user_iter
>   lib/iov_iter.c:24 [inline]
>   BUG: KMSAN: kernel-infoleak-after-free in iterate_ubuf
>   include/linux/iov_iter.h:29 [inline]
>   BUG: KMSAN: kernel-infoleak-after-free in iterate_and_advance2
>   include/linux/iov_iter.h:245 [inline]
>   BUG: KMSAN: kernel-infoleak-after-free in iterate_and_advance
>   include/linux/iov_iter.h:271 [inline]
>   BUG: KMSAN: kernel-infoleak-after-free in _copy_to_iter+0x364/0x2520
>   lib/iov_iter.c:186
>   instrument_copy_to_user include/linux/instrumented.h:114 [inline]
>    copy_to_user_iter lib/iov_iter.c:24 [inline]
>    iterate_ubuf include/linux/iov_iter.h:29 [inline]
>    iterate_and_advance2 include/linux/iov_iter.h:245 [inline]
>    iterate_and_advance include/linux/iov_iter.h:271 [inline]
>    _copy_to_iter+0x364/0x2520 lib/iov_iter.c:186
>    copy_to_iter include/linux/uio.h:197 [inline]
>    simple_copy_to_iter+0x68/0xa0 net/core/datagram.c:532
>    __skb_datagram_iter+0x123/0xdc0 net/core/datagram.c:420
>    skb_copy_datagram_iter+0x5c/0x200 net/core/datagram.c:546
>    skb_copy_datagram_msg include/linux/skbuff.h:3960 [inline]
>    packet_recvmsg+0xd9c/0x2000 net/packet/af_packet.c:3482
>    sock_recvmsg_nosec net/socket.c:1044 [inline]
>    sock_recvmsg net/socket.c:1066 [inline]
>    sock_read_iter+0x467/0x580 net/socket.c:1136
>    call_read_iter include/linux/fs.h:2014 [inline]
>    new_sync_read fs/read_write.c:389 [inline]
>    vfs_read+0x8f6/0xe00 fs/read_write.c:470
>    ksys_read+0x20f/0x4c0 fs/read_write.c:613
>    __do_sys_read fs/read_write.c:623 [inline]
>    __se_sys_read fs/read_write.c:621 [inline]
>    __x64_sys_read+0x93/0xd0 fs/read_write.c:621
>    do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>    do_syscall_64+0x44/0x110 arch/x86/entry/common.c:83
>    entry_SYSCALL_64_after_hwframe+0x63/0x6b
> 
>   Uninit was stored to memory at:
>    skb_put_data include/linux/skbuff.h:2622 [inline]
>    netlink_to_full_skb net/netlink/af_netlink.c:181 [inline]
>    __netlink_deliver_tap_skb net/netlink/af_netlink.c:298 [inline]
>    __netlink_deliver_tap+0x5be/0xc90 net/netlink/af_netlink.c:325
>    netlink_deliver_tap net/netlink/af_netlink.c:338 [inline]
>    netlink_deliver_tap_kernel net/netlink/af_netlink.c:347 [inline]
>    netlink_unicast_kernel net/netlink/af_netlink.c:1341 [inline]
>    netlink_unicast+0x10f1/0x1250 net/netlink/af_netlink.c:1368
>    netlink_sendmsg+0x1238/0x13d0 net/netlink/af_netlink.c:1910
>    sock_sendmsg_nosec net/socket.c:730 [inline]
>    __sock_sendmsg net/socket.c:745 [inline]
>    ____sys_sendmsg+0x9c2/0xd60 net/socket.c:2584
>    ___sys_sendmsg+0x28d/0x3c0 net/socket.c:2638
>    __sys_sendmsg net/socket.c:2667 [inline]
>    __do_sys_sendmsg net/socket.c:2676 [inline]
>    __se_sys_sendmsg net/socket.c:2674 [inline]
>    __x64_sys_sendmsg+0x307/0x490 net/socket.c:2674
>    do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>    do_syscall_64+0x44/0x110 arch/x86/entry/common.c:83
>    entry_SYSCALL_64_after_hwframe+0x63/0x6b
> 
>   Uninit was created at:
>    free_pages_prepare mm/page_alloc.c:1087 [inline]
>    free_unref_page_prepare+0xb0/0xa40 mm/page_alloc.c:2347
>    free_unref_page_list+0xeb/0x1100 mm/page_alloc.c:2533
>    release_pages+0x23d3/0x2410 mm/swap.c:1042
>    free_pages_and_swap_cache+0xd9/0xf0 mm/swap_state.c:316
>    tlb_batch_pages_flush mm/mmu_gather.c:98 [inline]
>    tlb_flush_mmu_free mm/mmu_gather.c:293 [inline]
>    tlb_flush_mmu+0x6f5/0x980 mm/mmu_gather.c:300
>    tlb_finish_mmu+0x101/0x260 mm/mmu_gather.c:392
>    exit_mmap+0x49e/0xd30 mm/mmap.c:3321
>    __mmput+0x13f/0x530 kernel/fork.c:1349
>    mmput+0x8a/0xa0 kernel/fork.c:1371
>    exit_mm+0x1b8/0x360 kernel/exit.c:567
>    do_exit+0xd57/0x4080 kernel/exit.c:858
>    do_group_exit+0x2fd/0x390 kernel/exit.c:1021
>    __do_sys_exit_group kernel/exit.c:1032 [inline]
>    __se_sys_exit_group kernel/exit.c:1030 [inline]
>    __x64_sys_exit_group+0x3c/0x50 kernel/exit.c:1030
>    do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>    do_syscall_64+0x44/0x110 arch/x86/entry/common.c:83
>    entry_SYSCALL_64_after_hwframe+0x63/0x6b
> 
>   Bytes 3852-3903 of 3904 are uninitialized
>   Memory access of size 3904 starts at ffff88812ea1e000
>   Data copied to user address 0000000020003280
> 
>   CPU: 1 PID: 5043 Comm: syz-executor297 Not tainted 6.7.0-rc5-syzkaller-00047-g5bd7ef53ffe5 #0
>   Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/10/2023
> 
> [Fix]
> 
> Mantic:	Clean cherry-pick from linux-6.6.y
> Jammy:	fix in Jammy via stable team
> Focal:	pending
> Bionic:	fix sent to esm ML
> Xenial:	fix sent to esm ML
> Trusty: not going to be fixed by us
> 
> [Test Case]
> 
> Compile and boot tested.
> 
> [Where problems could occur]
> 
> This fix affects those who use Netlink, an issue with this fix
> would be visable to the user via corrupted data or a system
> crash.
> 
> Ryosuke Yasuoka (1):
>    netlink: Fix kernel-infoleak-after-free in __skb_datagram_iter
> 
>   net/netlink/af_netlink.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 

Acked-by: Stefan Bader <stefan.bader at canonical.com>
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