CVE-2023-52772

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

afunix: fix use-after-free in unixstreamreadactor()

syzbot reported the following crash [1]

After releasing unix socket lock, u->oob_skb can be changed by another thread. We must temporarily increase skb refcount to make sure this other thread will not free the skb under us.

[1]

BUG: KASAN: slab-use-after-free in unixstreamreadactor+0xa7/0xc0 net/unix/afunix.c:2866 Read of size 4 at addr ffff88801f3b9cc4 by task syz-executor107/5297

CPU: 1 PID: 5297 Comm: syz-executor107 Not tainted 6.6.0-syzkaller-15910-gb8e3a87a627b #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/09/2023 Call Trace: <TASK> __dumpstack lib/dumpstack.c:88 [inline] dump_stacklvl+0xd9/0x1b0 lib/dumpstack.c:106 printaddressdescription mm/kasan/report.c:364 [inline] printreport+0xc4/0x620 mm/kasan/report.c:475 kasanreport+0xda/0x110 mm/kasan/report.c:588 unixstreamreadactor+0xa7/0xc0 net/unix/afunix.c:2866 unixstreamrecvurg net/unix/afunix.c:2587 [inline] unixstreamreadgeneric+0x19a5/0x2480 net/unix/afunix.c:2666 unixstreamrecvmsg+0x189/0x1b0 net/unix/afunix.c:2903 sockrecvmsgnosec net/socket.c:1044 [inline] sockrecvmsg+0xe2/0x170 net/socket.c:1066 ____sys_recvmsg+0x21f/0x5c0 net/socket.c:2803 ___sys_recvmsg+0x115/0x1a0 net/socket.c:2845 __sysrecvmsg+0x114/0x1e0 net/socket.c:2875 dosyscallx64 arch/x86/entry/common.c:51 [inline] dosyscall64+0x3f/0x110 arch/x86/entry/common.c:82 entrySYSCALL64afterhwframe+0x63/0x6b RIP: 0033:0x7fc67492c559 Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 51 18 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b0 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007fc6748ab228 EFLAGS: 00000246 ORIGRAX: 000000000000002f RAX: ffffffffffffffda RBX: 000000000000001c RCX: 00007fc67492c559 RDX: 0000000040010083 RSI: 0000000020000140 RDI: 0000000000000004 RBP: 00007fc6749b6348 R08: 00007fc6748ab6c0 R09: 00007fc6748ab6c0 R10: 0000000000000000 R11: 0000000000000246 R12: 00007fc6749b6340 R13: 00007fc6749b634c R14: 00007ffe9fac52a0 R15: 00007ffe9fac5388 </TASK>

Allocated by task 5295: kasansavestack+0x33/0x50 mm/kasan/common.c:45 kasansettrack+0x25/0x30 mm/kasan/common.c:52 __kasanslaballoc+0x81/0x90 mm/kasan/common.c:328 kasanslaballoc include/linux/kasan.h:188 [inline] slabpostallochook mm/slab.h:763 [inline] slaballocnode mm/slub.c:3478 [inline] kmemcacheallocnode+0x180/0x3c0 mm/slub.c:3523 __allocskb+0x287/0x330 net/core/skbuff.c:641 allocskb include/linux/skbuff.h:1286 [inline] allocskbwithfrags+0xe4/0x710 net/core/skbuff.c:6331 sockallocsendpskb+0x7e4/0x970 net/core/sock.c:2780 sockallocsendskb include/net/sock.h:1884 [inline] queueoob net/unix/afunix.c:2147 [inline] unixstreamsendmsg+0xb5f/0x10a0 net/unix/afunix.c:2301 socksendmsgnosec net/socket.c:730 [inline] __sock_sendmsg+0xd5/0x180 net/socket.c:745 ____sys_sendmsg+0x6ac/0x940 net/socket.c:2584 ___sys_sendmsg+0x135/0x1d0 net/socket.c:2638 _syssendmsg+0x117/0x1e0 net/socket.c:2667 dosyscallx64 arch/x86/entry/common.c:51 [inline] dosyscall64+0x3f/0x110 arch/x86/entry/common.c:82 entrySYSCALL64afterhwframe+0x63/0x6b

Freed by task 5295: kasansavestack+0x33/0x50 mm/kasan/common.c:45 kasansettrack+0x25/0x30 mm/kasan/common.c:52 kasansavefree_info+0x2b/0x40 mm/kasan/generic.c:522 ____kasanslabfree mm/kasan/common.c:236 [inline] ____kasanslabfree+0x15b/0x1b0 mm/kasan/common.c:200 kasanslabfree include/linux/kasan.h:164 [inline] slab_freehook mm/slub.c:1800 [inline] slabfreefreelisthook+0x114/0x1e0 mm/slub.c:1826 slabfree mm/slub.c:3809 [inline] kmemcachefree+0xf8/0x340 mm/slub.c:3831 kfreeskbmem+0xef/0x1b0 net/core/skbuff.c:1015 _kfreeskb net/core/skbuff.c:1073 [inline] consumeskb net/core/skbuff.c:1288 [inline] consumeskb+0xdf/0x170 net/core/skbuff.c:1282 queueoob net/unix/afunix.c:2178 [inline] u ---truncated---