CVE-2024-26636: llc: make llc_ui_sendmsg() more robust against bonding changes

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

llc: make llcuisendmsg() more robust against bonding changes

syzbot was able to trick llcuisendmsg(), allocating an skb with no headroom, but subsequently trying to push 14 bytes of Ethernet header [1]

Like some others, llcuisendmsg() releases the socket lock before calling sockallocsendskb(). Then it acquires it again, but does not redo all the sanity checks that were performed.

This fix:

- Uses LLRESERVEDSPACE() to reserve space. - Check all conditions again after socket lock is held again. - Do not account Ethernet header for mtu limitation.

[1]

skbuff: skbunderpanic: text:ffff800088baa334 len:1514 put:14 head:ffff0000c9c37000 data:ffff0000c9c36ff2 tail:0x5dc end:0x6c0 dev:bond0

kernel BUG at net/core/skbuff.c:193 ! Internal error: Oops - BUG: 00000000f2000800 [#1] PREEMPT SMP Modules linked in: CPU: 0 PID: 6875 Comm: syz-executor.0 Not tainted 6.7.0-rc8-syzkaller-00101-g0802e17d9aca-dirty #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023 pstate: 60400005 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--) pc : skbpanic net/core/skbuff.c:189 [inline] pc : skbunderpanic+0x13c/0x140 net/core/skbuff.c:203 lr : skbpanic net/core/skbuff.c:189 [inline] lr : skbunderpanic+0x13c/0x140 net/core/skbuff.c:203 sp : ffff800096f97000 x29: ffff800096f97010 x28: ffff80008cc8d668 x27: dfff800000000000 x26: ffff0000cb970c90 x25: 00000000000005dc x24: ffff0000c9c36ff2 x23: ffff0000c9c37000 x22: 00000000000005ea x21: 00000000000006c0 x20: 000000000000000e x19: ffff800088baa334 x18: 1fffe000368261ce x17: ffff80008e4ed000 x16: ffff80008a8310f8 x15: 0000000000000001 x14: 1ffff00012df2d58 x13: 0000000000000000 x12: 0000000000000000 x11: 0000000000000001 x10: 0000000000ff0100 x9 : e28a51f1087e8400 x8 : e28a51f1087e8400 x7 : ffff80008028f8d0 x6 : 0000000000000000 x5 : 0000000000000001 x4 : 0000000000000001 x3 : ffff800082b78714 x2 : 0000000000000001 x1 : 0000000100000000 x0 : 0000000000000089 Call trace: skbpanic net/core/skbuff.c:189 [inline] skbunderpanic+0x13c/0x140 net/core/skbuff.c:203 skbpush+0xf0/0x108 net/core/skbuff.c:2451 ethheader+0x44/0x1f8 net/ethernet/eth.c:83 devhardheader include/linux/netdevice.h:3188 [inline] llcmachdrinit+0x110/0x17c net/llc/llcoutput.c:33 llcsapactionsendxidc+0x170/0x344 net/llc/llcsac.c:85 llcexecsaptransactions net/llc/llcsap.c:153 [inline] llcsapnextstate net/llc/llcsap.c:182 [inline] llcsapstateprocess+0x1ec/0x774 net/llc/llcsap.c:209 llcbuildandsendxidpkt+0x12c/0x1c0 net/llc/llcsap.c:270 llcuisendmsg+0x7bc/0xb1c net/llc/afllc.c:997 socksendmsgnosec net/socket.c:730 [inline] socksendmsg net/socket.c:745 [inline] socksendmsg+0x194/0x274 net/socket.c:767 splicetosocket+0x7cc/0xd58 fs/splice.c:881 dosplicefrom fs/splice.c:933 [inline] directspliceactor+0xe4/0x1c0 fs/splice.c:1142 splicedirecttoactor+0x2a0/0x7e4 fs/splice.c:1088 dosplicedirect+0x20c/0x348 fs/splice.c:1194 dosendfile+0x4bc/0xc70 fs/readwrite.c:1254 dosyssendfile64 fs/readwrite.c:1322 [inline] sesyssendfile64 fs/readwrite.c:1308 [inline] arm64syssendfile64+0x160/0x3b4 fs/readwrite.c:1308 invokesyscall arch/arm64/kernel/syscall.c:37 [inline] invokesyscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:51 el0svccommon+0x130/0x23c arch/arm64/kernel/syscall.c:136 doel0svc+0x48/0x58 arch/arm64/kernel/syscall.c:155 el0svc+0x54/0x158 arch/arm64/kernel/entry-common.c:678 el0t64synchandler+0x84/0xfc arch/arm64/kernel/entry-common.c:696 el0t64sync+0x190/0x194 arch/arm64/kernel/entry.S:595 Code: aa1803e6 aa1903e7 a90023f5 94792f6a (d4210000)