CVE-2024-26805

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
—truncated—