[syzbot] [fs?] KASAN: stack-out-of-bounds Read in proc_pid_stack

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 950b879b7f02 riscv: Fixup race condition on PG_dcache_clea..
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/riscv/linux.git fixes
console output: https://syzkaller.appspot.com/x/log.txt?x=10c4c1f7c80000
kernel config: https://syzkaller.appspot.com/x/.config?x=ecebece1b90c0342
dashboard link: https://syzkaller.appspot.com/bug?extid=01e9a564dc6b3289cea3
compiler: riscv64-linux-gnu-gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
userspace arch: riscv64

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+01e9a5...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: stack-out-of-bounds in walk_stackframe+0x128/0x2fe arch/riscv/kernel/stacktrace.c:58
Read of size 8 at addr ff200000030a79b0 by task syz-executor.1/7894

CPU: 0 PID: 7894 Comm: syz-executor.1 Tainted: G W 6.2.0-rc1-syzkaller #0
Hardware name: riscv-virtio,qemu (DT)
Call Trace:
[<ffffffff8000b9ea>] dump_backtrace+0x2e/0x3c arch/riscv/kernel/stacktrace.c:121
[<ffffffff83402b96>] show_stack+0x34/0x40 arch/riscv/kernel/stacktrace.c:127
[<ffffffff83442726>] __dump_stack lib/dump_stack.c:88 [inline]
[<ffffffff83442726>] dump_stack_lvl+0xe0/0x14c lib/dump_stack.c:106
[<ffffffff83409674>] print_address_description mm/kasan/report.c:306 [inline]
[<ffffffff83409674>] print_report+0x1e4/0x4c0 mm/kasan/report.c:417
[<ffffffff804ead14>] kasan_report+0xb8/0xe6 mm/kasan/report.c:517
[<ffffffff804ebea4>] check_region_inline mm/kasan/generic.c:183 [inline]
[<ffffffff804ebea4>] __asan_load8+0x7e/0xa6 mm/kasan/generic.c:256
[<ffffffff8000b782>] walk_stackframe+0x128/0x2fe arch/riscv/kernel/stacktrace.c:58
[<ffffffff8000bc66>] arch_stack_walk+0x2c/0x3c arch/riscv/kernel/stacktrace.c:154
[<ffffffff80190822>] stack_trace_save_tsk+0x14a/0x1bc kernel/stacktrace.c:150
[<ffffffff80697822>] proc_pid_stack+0x146/0x1ee fs/proc/base.c:456
[<ffffffff80698bb0>] proc_single_show+0x9c/0x148 fs/proc/base.c:777
[<ffffffff805af580>] traverse.part.0+0x74/0x2ca fs/seq_file.c:111
[<ffffffff805aff02>] traverse fs/seq_file.c:101 [inline]
[<ffffffff805aff02>] seq_read_iter+0x72c/0x934 fs/seq_file.c:195
[<ffffffff805b0224>] seq_read+0x11a/0x16e fs/seq_file.c:162
[<ffffffff805453ea>] do_loop_readv_writev fs/read_write.c:756 [inline]
[<ffffffff805453ea>] do_loop_readv_writev fs/read_write.c:743 [inline]
[<ffffffff805453ea>] do_iter_read+0x324/0x3c2 fs/read_write.c:798
[<ffffffff805455f8>] vfs_readv+0xfe/0x166 fs/read_write.c:916
[<ffffffff80549c66>] do_preadv fs/read_write.c:1008 [inline]
[<ffffffff80549c66>] __do_sys_preadv fs/read_write.c:1058 [inline]
[<ffffffff80549c66>] sys_preadv+0x182/0x1fa fs/read_write.c:1053
[<ffffffff80005ff6>] ret_from_syscall+0x0/0x2

The buggy address belongs to the virtual mapping at
[ff200000030a0000, ff200000030a9000) created by:
kernel_clone+0xee/0x914 kernel/fork.c:2681

The buggy address belongs to the physical page:
page:ff1c0000024e5f00 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x9397c
memcg:ff6000000ffd7202
flags: 0xffe000000000000(node=0|zone=0|lastcpupid=0x7ff)
raw: 0ffe000000000000 0000000000000000 0000000000000122 0000000000000000
raw: 0000000000000000 0000000000000000 00000001ffffffff ff6000000ffd7202
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0x102dc2(GFP_HIGHUSER|__GFP_NOWARN|__GFP_ZERO), pid 7873, tgid 7873 (syz-executor.1), ts 4012100669800, free_ts 4010400733200
__set_page_owner+0x32/0x182 mm/page_owner.c:190
set_page_owner include/linux/page_owner.h:31 [inline]
post_alloc_hook+0xf8/0x11a mm/page_alloc.c:2524
prep_new_page mm/page_alloc.c:2531 [inline]
get_page_from_freelist+0xc0e/0x1118 mm/page_alloc.c:4283
__alloc_pages+0x1b0/0x165a mm/page_alloc.c:5549
alloc_pages+0x132/0x25e mm/mempolicy.c:2286
vm_area_alloc_pages mm/vmalloc.c:2989 [inline]
__vmalloc_area_node mm/vmalloc.c:3057 [inline]
__vmalloc_node_range+0x81c/0xdb4 mm/vmalloc.c:3227
alloc_thread_stack_node kernel/fork.c:311 [inline]
dup_task_struct kernel/fork.c:987 [inline]
copy_process+0x210e/0x4068 kernel/fork.c:2097
kernel_clone+0xee/0x914 kernel/fork.c:2681
__do_sys_clone+0xec/0x120 kernel/fork.c:2822
sys_clone+0x32/0x44 kernel/fork.c:2790
ret_from_syscall+0x0/0x2
page last free stack trace:
__reset_page_owner+0x4a/0xf8 mm/page_owner.c:148
reset_page_owner include/linux/page_owner.h:24 [inline]
free_pages_prepare mm/page_alloc.c:1446 [inline]
free_pcp_prepare+0x254/0x48e mm/page_alloc.c:1496
free_unref_page_prepare mm/page_alloc.c:3369 [inline]
free_unref_page_list+0x11e/0x736 mm/page_alloc.c:3510
release_pages+0x85a/0xbb2 mm/swap.c:1076
free_pages_and_swap_cache+0x76/0x88 mm/swap_state.c:311
tlb_batch_pages_flush+0x86/0x10c mm/mmu_gather.c:97
tlb_flush_mmu_free mm/mmu_gather.c:292 [inline]
tlb_flush_mmu mm/mmu_gather.c:299 [inline]
tlb_finish_mmu+0xcc/0x280 mm/mmu_gather.c:391
exit_mmap+0x190/0x686 mm/mmap.c:3096
__mmput+0x98/0x290 kernel/fork.c:1207
mmput+0x74/0x88 kernel/fork.c:1229
exit_mm kernel/exit.c:563 [inline]
do_exit+0x602/0x17be kernel/exit.c:854
do_group_exit+0x8e/0x15e kernel/exit.c:1012
__do_sys_exit_group kernel/exit.c:1023 [inline]
__wake_up_parent+0x0/0x4a kernel/exit.c:1021
ret_from_syscall+0x0/0x2

Memory state around the buggy address:
ff200000030a7880: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ff200000030a7900: 00 00 00 00 00 00 00 00 f1 f1 f1 f1 00 00 f2 f2
>ff200000030a7980: 00 00 00 f3 f3 f3 f3 f3 00 00 00 00 00 00 00 00
^
ff200000030a7a00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ff200000030a7a80: 00 00 00 00 00 00 00 00 00 00 00 00 f1 f1 f1 f1
==================================================================


---
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[Dmitry Vyukov]

+riscv maintainers

I think this is an issue in riscv stack walking.
If it's imprecise or walks stacks of running tasks, it needs to use
READ_ONCE_NOCHECK.

#syz set subsystems: riscv

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[Alexandre Ghiti]

This fix was merged in 6.3: commit 76950340cf03 ("riscv: Use
READ_ONCE_NOCHECK in imprecise unwinding stack mode").

> _______________________________________________
> linux-riscv mailing list
> linux...@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv

[Dmitry Vyukov]

Oh, I see, syzbot riscv build is still broken due to:
https://syzkaller.appspot.com/bug?id=502e4cca2c3c985c2125ffa945b8e636b7b100d7
https://lore.kernel.org/all/00000000000049...@google.com/T/#md2075a04dd463fefe31f73e098672a69d948a1ce

so it still tests an older build.

#syz fix:

riscv: Use READ_ONCE_NOCHECK in imprecise unwinding stack mode

[Conor Dooley]

I think this one is correct, but

> https://lore.kernel.org/all/00000000000049...@google.com/T/#md2075a04dd463fefe31f73e098672a69d948a1ce

this isn't the right lore link. I think you meant:
https://lore.kernel.org/linux-riscv/CANp29Y5dbsSjd5q2TNJYgO5U...@mail.gmail.com/

The fix for that went through the bpf tree though:
https://lore.kernel.org/bpf/871qkh9...@all.your.base.are.belong.to.us/T/

Perhaps that is now fixed in mainline? I think riscv/fixes just needs to
be updated (it normally is after -rc1 I think) and things should be
good to go, no?

Cheers,
Conor.

[Dmitry Vyukov]

> The fix for that was merged in 6.3-rc2 too (commit 2d311f480b52
> ("riscv, bpf: Fix patch_text implicit declaration")): but the fixes
> branch is still based on top of Linux 6.3-rc1 (Aleksandr mentioned
> that already).

Is riscv-fixes the right branch to test?
Is there one that is updated regularly?
syzbot generally requires a fresh tree. Provided there are dozens of
bugs being found and fixed every week, if a tree becomes too old, it
just produces already fixed bugs that waste time.

https://lore.kernel.org/all/00000000000049...@google.com/T/#md2075a04dd463fefe31f73e098672a69d948a1ce
>
> That's weird, I think this one was merged in v6.1-rc2 (commit
> 5c20a3a9df19 ("RISC-V: Fix compilation without RISCV_ISA_ZICBOM")).

>
> >
> > so it still tests an older build.
>

> FYI, the latest fixes for KASAN were merged in 6.4 (or are about to).
>
> Thanks,
>
> Alex

[Alexandre Ghiti]

The fix for that was merged in 6.3-rc2 too (commit 2d311f480b52
("riscv, bpf: Fix patch_text implicit declaration")): but the fixes
branch is still based on top of Linux 6.3-rc1 (Aleksandr mentioned
that already).

> https://lore.kernel.org/all/00000000000049...@google.com/T/#md2075a04dd463fefe31f73e098672a69d948a1ce

That's weird, I think this one was merged in v6.1-rc2 (commit
5c20a3a9df19 ("RISC-V: Fix compilation without RISCV_ISA_ZICBOM")).

>

> so it still tests an older build.

FYI, the latest fixes for KASAN were merged in 6.4 (or are about to).

Thanks,

Alex

>

[Alexandre Ghiti]

I would say that testing only the latest rcX is the best bet for us as
the fixes branch always lags on rc1, but @Palmer/@Conor may have
another opinion.