CVE-2024-26805: netlink: Fix kernel-infoleak-after-free in __skb_datagram_iter

In the Linux kernel, the following vulnerability has been resolved:

netlink: Fix kernel-infoleak-after-free in skbdatagramiter

syzbot reported the following uninit-value access issue [1]:

netlinktofullskb() creates a new skb and puts the skb->data passed as a 1st arg of netlinktofullskb() onto new skb. The data size is specified as len and passed to skbputdata(). 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 instrumentcopytouser include/linux/instrumented.h:114 [inline] BUG: KMSAN: kernel-infoleak-after-free in copytouseriter lib/ioviter.c:24 [inline] BUG: KMSAN: kernel-infoleak-after-free in iterateubuf include/linux/ioviter.h:29 [inline] BUG: KMSAN: kernel-infoleak-after-free in iterateandadvance2 include/linux/ioviter.h:245 [inline] BUG: KMSAN: kernel-infoleak-after-free in iterateandadvance include/linux/ioviter.h:271 [inline] BUG: KMSAN: kernel-infoleak-after-free in copytoiter+0x364/0x2520 lib/ioviter.c:186 instrumentcopytouser include/linux/instrumented.h:114 [inline] copytouseriter lib/ioviter.c:24 [inline] iterateubuf include/linux/ioviter.h:29 [inline] iterateandadvance2 include/linux/ioviter.h:245 [inline] iterateandadvance include/linux/ioviter.h:271 [inline] copytoiter+0x364/0x2520 lib/ioviter.c:186 copytoiter include/linux/uio.h:197 [inline] simplecopytoiter+0x68/0xa0 net/core/datagram.c:532 skbdatagramiter+0x123/0xdc0 net/core/datagram.c:420 skbcopydatagramiter+0x5c/0x200 net/core/datagram.c:546 skbcopydatagrammsg include/linux/skbuff.h:3960 [inline] packetrecvmsg+0xd9c/0x2000 net/packet/afpacket.c:3482 sockrecvmsgnosec net/socket.c:1044 [inline] sockrecvmsg net/socket.c:1066 [inline] sockreaditer+0x467/0x580 net/socket.c:1136 callreaditer include/linux/fs.h:2014 [inline] newsyncread fs/readwrite.c:389 [inline] vfsread+0x8f6/0xe00 fs/readwrite.c:470 ksysread+0x20f/0x4c0 fs/readwrite.c:613 dosysread fs/readwrite.c:623 [inline] sesysread fs/readwrite.c:621 [inline] x64sysread+0x93/0xd0 fs/readwrite.c:621 dosyscallx64 arch/x86/entry/common.c:52 [inline] dosyscall64+0x44/0x110 arch/x86/entry/common.c:83 entrySYSCALL64afterhwframe+0x63/0x6b

Uninit was stored to memory at: skbputdata include/linux/skbuff.h:2622 [inline] netlinktofullskb net/netlink/afnetlink.c:181 [inline] netlinkdelivertapskb net/netlink/afnetlink.c:298 [inline] netlinkdelivertap+0x5be/0xc90 net/netlink/afnetlink.c:325 netlinkdelivertap net/netlink/afnetlink.c:338 [inline] netlinkdelivertapkernel net/netlink/afnetlink.c:347 [inline] netlinkunicastkernel net/netlink/afnetlink.c:1341 [inline] netlinkunicast+0x10f1/0x1250 net/netlink/afnetlink.c:1368 netlinksendmsg+0x1238/0x13d0 net/netlink/afnetlink.c:1910 socksendmsgnosec net/socket.c:730 [inline] socksendmsg net/socket.c:745 [inline] syssendmsg+0x9c2/0xd60 net/socket.c:2584 syssendmsg+0x28d/0x3c0 net/socket.c:2638 syssendmsg net/socket.c:2667 [inline] dosyssendmsg net/socket.c:2676 [inline] sesyssendmsg net/socket.c:2674 [inline] x64syssendmsg+0x307/0x490 net/socket.c:2674 dosyscallx64 arch/x86/entry/common.c:52 [inline] dosyscall64+0x44/0x110 arch/x86/entry/common.c:83 entrySYSCALL64afterhwframe+0x63/0x6b

Uninit was created at: freepagesprepare mm/pagealloc.c:1087 [inline] freeunrefpageprepare+0xb0/0xa40 mm/pagealloc.c:2347 freeunrefpagelist+0xeb/0x1100 mm/pagealloc.c:2533 releasepages+0x23d3/0x2410 mm/swap.c:1042 freepagesandswapcache+0xd9/0xf0 mm/swapstate.c:316 tlbbatchpages ---truncated---