Re: [syzbot] [bpf?] [net?] BUG: unable to handle kernel NULL pointer dereference in sk_msg_recvmsg

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
BUG: unable to handle kernel NULL pointer dereference in sk_msg_recvmsg

Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
Mem abort info:
  ESR = 0x0000000096000006
  EC = 0x25: DABT (current EL), IL = 32 bits
  SET = 0, FnV = 0
  EA = 0, S1PTW = 0
  FSC = 0x06: level 2 translation fault
Data abort info:
  ISV = 0, ISS = 0x00000006, ISS2 = 0x00000000
  CM = 0, WnR = 0, TnD = 0, TagAccess = 0
  GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
user pgtable: 4k pages, 48-bit VAs, pgdp=0000000043940000
[0000000000000000] pgd=08000000468bd003, p4d=08000000468bd003, pud=0800000046ab8003, pmd=0000000000000000
Internal error: Oops: 0000000096000006 [#1] PREEMPT SMP
Modules linked in:
CPU: 1 PID: 3479 Comm: syz-executor.0 Not tainted 6.9.0-rc4-syzkaller-g96fca68c4fbf #0
Hardware name: linux,dummy-virt (DT)
pstate: 61401009 (nZCv daif +PAN -UAO -TCO +DIT +SSBS BTYPE=--)
pc : page_kasan_tag include/linux/mm.h:1834 [inline]
pc : lowmem_page_address include/linux/mm.h:2234 [inline]
pc : kmap_local_page include/linux/highmem-internal.h:185 [inline]
pc : copy_page_to_iter+0xb4/0x154 lib/iov_iter.c:360
lr : sk_msg_recvmsg+0xf8/0x37c net/core/skmsg.c:437
sp : ffff80008964b940
x29: ffff80008964b940 x28: 0000000000000000 x27: f1ff000005cd9800
x26: 0000000000000000 x25: 0000000000000000 x24: 0000000000000000
x23: 0000000000000000 x22: 0000020040000000 x21: ffff000000000000
x20: 0000000000001000 x19: ffff80008964bd50 x18: 0000000000000000
x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000000
x14: 0000000000000382 x13: 0000000000000000 x12: 0000000000000000
x11: 0000000000000001 x10: 382d7d5bed6f0326 x9 : a9c46d8380c16462
x8 : fdff0000056d6bc8 x7 : 0000000000000000 x6 : fdff000005cd6d40
x5 : 0000000000000001 x4 : 0000000000000000 x3 : ffff80008964bd50
x2 : 0000000000000000 x1 : 0000000000000000 x0 : ffff801000000000
Call trace:
 arch_static_branch_jump arch/arm64/include/asm/jump_label.h:38 [inline]
 kasan_enabled include/linux/kasan-enabled.h:13 [inline]
 page_kasan_tag include/linux/mm.h:1833 [inline]
 lowmem_page_address include/linux/mm.h:2234 [inline]
 kmap_local_page include/linux/highmem-internal.h:185 [inline]
 copy_page_to_iter+0xb4/0x154 lib/iov_iter.c:360
 sk_msg_recvmsg+0xf8/0x37c net/core/skmsg.c:437
 unix_bpf_recvmsg net/unix/unix_bpf.c:73 [inline]
 unix_bpf_recvmsg+0x13c/0x4f0 net/unix/unix_bpf.c:50
 unix_dgram_recvmsg+0x30/0x4c net/unix/af_unix.c:2529
 sock_recvmsg_nosec net/socket.c:1046 [inline]
 sock_recvmsg net/socket.c:1068 [inline]
 sock_recvmsg net/socket.c:1064 [inline]
 ____sys_recvmsg+0x1d0/0x268 net/socket.c:2803
 ___sys_recvmsg+0x90/0xe8 net/socket.c:2845
 do_recvmmsg+0xc8/0x2f8 net/socket.c:2939
 __sys_recvmmsg net/socket.c:3018 [inline]
 __do_sys_recvmmsg net/socket.c:3041 [inline]
 __se_sys_recvmmsg net/socket.c:3034 [inline]
 __arm64_sys_recvmmsg+0xd0/0xec net/socket.c:3034
 __invoke_syscall arch/arm64/kernel/syscall.c:34 [inline]
 invoke_syscall+0x48/0x118 arch/arm64/kernel/syscall.c:48
 el0_svc_common.constprop.0+0x40/0xe0 arch/arm64/kernel/syscall.c:133
 do_el0_svc+0x1c/0x28 arch/arm64/kernel/syscall.c:152
 el0_svc+0x34/0xf8 arch/arm64/kernel/entry-common.c:712
 el0t_64_sync_handler+0x100/0x12c arch/arm64/kernel/entry-common.c:730
 el0t_64_sync+0x19c/0x1a0 arch/arm64/kernel/entry.S:598
Code: 8b160320 d346fc00 8b0032a0 d503201f (f9400323) 
---[ end trace 0000000000000000 ]---
----------------
Code disassembly (best guess):
   0:	8b160320 	add	x0, x25, x22
   4:	d346fc00 	lsr	x0, x0, #6
   8:	8b0032a0 	add	x0, x21, x0, lsl #12
   c:	d503201f 	nop
* 10:	f9400323 	ldr	x3, [x25] <-- trapping instruction


Tested on:

commit:         96fca68c Merge tag 'nfsd-6.9-3' of git://git.kernel.or..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16572cc3180000
kernel config:  https://syzkaller.appspot.com/x/.config?x=4ba795506e24be71
dashboard link: https://syzkaller.appspot.com/bug?extid=84f695756ed0c4bb3aba
compiler:       aarch64-linux-gnu-gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
userspace arch: arm64

Note: no patches were applied.