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[PATCH 1/2] mm/huge_memory: skip invalid debugfs file entry for folio split
mcgrof at kernel
Apr 24, 2024, 3:54 PM
Post #1 of 6 (18 views)
Permalink
If the file entry is too long we may easily end up going out of bounds
and crash after strsep() on sscanf(). To avoid this ensure we bound the
string to an expected length before we use sscanf() on it.

Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
---
mm/huge_memory.c | 9 +++++++++
1 file changed, 9 insertions(+)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 9e9879d2f501..8386d24a163e 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3623,6 +3623,7 @@ static ssize_t split_huge_pages_write(struct file *file, const char __user *buf,
char file_path[MAX_INPUT_BUF_SZ];
pgoff_t off_start = 0, off_end = 0;
size_t input_len = strlen(input_buf);
+ size_t max_left_over;

tok = strsep(&buf, ",");
if (tok) {
@@ -3632,6 +3633,14 @@ static ssize_t split_huge_pages_write(struct file *file, const char __user *buf,
goto out;
}

+ max_left_over = MAX_INPUT_BUF_SZ - strlen(file_path);
+ if (!buf ||
+ strnlen(buf, max_left_over) < 7 ||
+ strnlen(buf, max_left_over) > max_left_over) {
+ ret = -EINVAL;
+ goto out;
+ }
+
ret = sscanf(buf, "0x%lx,0x%lx,%d", &off_start, &off_end, &new_order);
if (ret != 2 && ret != 3) {
ret = -EINVAL;
--
2.43.0
Re: [PATCH 1/2] mm/huge_memory: skip invalid debugfs file entry for folio split [ In reply to ]
ziy at nvidia
Apr 24, 2024, 6:03 PM
Post #2 of 6 (16 views)
Permalink
On 24 Apr 2024, at 18:54, Luis Chamberlain wrote:

> If the file entry is too long we may easily end up going out of bounds
> and crash after strsep() on sscanf(). To avoid this ensure we bound the
> string to an expected length before we use sscanf() on it.
>
> Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
> ---
> mm/huge_memory.c | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 9e9879d2f501..8386d24a163e 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -3623,6 +3623,7 @@ static ssize_t split_huge_pages_write(struct file *file, const char __user *buf,
> char file_path[MAX_INPUT_BUF_SZ];
> pgoff_t off_start = 0, off_end = 0;
> size_t input_len = strlen(input_buf);
> + size_t max_left_over;
>
> tok = strsep(&buf, ",");
> if (tok) {
> @@ -3632,6 +3633,14 @@ static ssize_t split_huge_pages_write(struct file *file, const char __user *buf,
> goto out;
> }
>
> + max_left_over = MAX_INPUT_BUF_SZ - strlen(file_path);
> + if (!buf ||
> + strnlen(buf, max_left_over) < 7 ||

What is this magic number 7? strlen("0xN,0xN") as the minimal input string size?
Maybe use sizeof("0xN,0xN") - 1 instead?

> + strnlen(buf, max_left_over) > max_left_over) {
> + ret = -EINVAL;
> + goto out;
> + }
> +
> ret = sscanf(buf, "0x%lx,0x%lx,%d", &off_start, &off_end, &new_order);
> if (ret != 2 && ret != 3) {
> ret = -EINVAL;
> --
> 2.43.0

Everything else looks good to me. Reviewed-by: Zi Yan <ziy@nvidia.com>

--
Best Regards,
Yan, Zi

Attached Files:

Re: [PATCH 1/2] mm/huge_memory: skip invalid debugfs file entry for folio split [ In reply to ]
akpm at linux-foundation
Apr 25, 2024, 2:01 PM
Post #3 of 6 (13 views)
Permalink
On Wed, 24 Apr 2024 15:54:48 -0700 Luis Chamberlain <mcgrof@kernel.org> wrote:

> If the file entry is too long we may easily end up going out of bounds
> and crash after strsep() on sscanf().
>

Can you explain why? I'm not seeing it.
Re: [PATCH 1/2] mm/huge_memory: skip invalid debugfs file entry for folio split [ In reply to ]
mcgrof at kernel
Apr 25, 2024, 3:40 PM
Post #4 of 6 (13 views)
Permalink
On Wed, Apr 24, 2024 at 09:03:51PM -0400, Zi Yan wrote:
> On 24 Apr 2024, at 18:54, Luis Chamberlain wrote:
>
> > If the file entry is too long we may easily end up going out of bounds
> > and crash after strsep() on sscanf(). To avoid this ensure we bound the
> > string to an expected length before we use sscanf() on it.
> >
> > Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
> > ---
> > mm/huge_memory.c | 9 +++++++++
> > 1 file changed, 9 insertions(+)
> >
> > diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> > index 9e9879d2f501..8386d24a163e 100644
> > --- a/mm/huge_memory.c
> > +++ b/mm/huge_memory.c
> > @@ -3623,6 +3623,7 @@ static ssize_t split_huge_pages_write(struct file *file, const char __user *buf,
> > char file_path[MAX_INPUT_BUF_SZ];
> > pgoff_t off_start = 0, off_end = 0;
> > size_t input_len = strlen(input_buf);
> > + size_t max_left_over;
> >
> > tok = strsep(&buf, ",");
> > if (tok) {
> > @@ -3632,6 +3633,14 @@ static ssize_t split_huge_pages_write(struct file *file, const char __user *buf,
> > goto out;
> > }
> >
> > + max_left_over = MAX_INPUT_BUF_SZ - strlen(file_path);
> > + if (!buf ||
> > + strnlen(buf, max_left_over) < 7 ||
>
> What is this magic number 7? strlen("0xN,0xN") as the minimal input string size?
> Maybe use sizeof("0xN,0xN") - 1 instead?

Sure and I forgot the fixes tag, will send a v2.

Luis
Re: [PATCH 1/2] mm/huge_memory: skip invalid debugfs file entry for folio split [ In reply to ]
mcgrof at kernel
Apr 28, 2024, 9:04 PM
Post #5 of 6 (6 views)
Permalink
On Thu, Apr 25, 2024 at 02:01:26PM -0700, Andrew Morton wrote:
> On Wed, 24 Apr 2024 15:54:48 -0700 Luis Chamberlain <mcgrof@kernel.org> wrote:
>
> > If the file entry is too long we may easily end up going out of bounds
> > and crash after strsep() on sscanf().
> >
>
> Can you explain why? I'm not seeing it.

I couldn't see it either but I just looked at the crash below and
its the only thing I could think of. So I think its when userspace
somehow abuses MAX_INPUT_BUF_SZ a lot somehow.

The test I am using:

https://lore.kernel.org/all/20240424224649.1494092-1-mcgrof@kernel.org/

The crash:

Apr 28 20:09:21 debian12-xfs-reflink-16k-4ks unknown: run fstests generic/745 at 2024-04-28 20:09:21
Apr 28 20:09:22 debian12-xfs-reflink-16k-4ks kernel: XFS (loop5): EXPERIMENTAL: Filesystem with Large Block Size (16384 bytes) enabled.
Apr 28 20:09:22 debian12-xfs-reflink-16k-4ks kernel: XFS (loop5): Mounting V5 Filesystem 6633551d-bd66-4a7c-a4ce-7e312e611742
Apr 28 20:09:22 debian12-xfs-reflink-16k-4ks kernel: XFS (loop5): Ending clean mount
Apr 28 20:09:25 debian12-xfs-reflink-16k-4ks kernel: huge_memory: split file-backed THPs in file: /media/scratch/test/fss896, page offset: [0x0 - 0x0] with order: 2
Apr 28 20:09:25 debian12-xfs-reflink-16k-4ks kernel: huge_memory: 0 of 0 file-backed THP split
Apr 28 20:09:25 debian12-xfs-reflink-16k-4ks kernel: huge_memory: split file-backed THPs in file: /media/scratch/test/p0/f0, page offset: [0x0 - 0x6a4000] with order: 2
Apr 28 20:09:25 debian12-xfs-reflink-16k-4ks kernel: huge_memory: 0 of 2 file-backed THP split
Apr 28 20:09:25 debian12-xfs-reflink-16k-4ks kernel: huge_memory: split file-backed THPs in file: /media/scratch/test/p0/f1, page offset: [0x0 - 0x0] with order: 2
Apr 28 20:09:25 debian12-xfs-reflink-16k-4ks kernel: huge_memory: 0 of 0 file-backed THP split
Apr 28 20:09:25 debian12-xfs-reflink-16k-4ks kernel: huge_memory: split file-backed THPs in file: /media/scratch/test/p2/d0/d1/d4/f5, page offset: [0x0 - 0xc83d64] with order: 2
Apr 28 20:09:25 debian12-xfs-reflink-16k-4ks kernel: huge_memory: 1 of 6 file-backed THP split
Apr 28 20:09:25 debian12-xfs-reflink-16k-4ks kernel: huge_memory: split file-backed THPs in file: /media/scratch/test/p2/d0/d1/d4/f9, page offset: [0x0 - 0xcad301] with order: 2
Apr 28 20:09:25 debian12-xfs-reflink-16k-4ks kernel: huge_memory: 9 of 79 file-backed THP split


<--- after ~2 minutes -->

Apr 28 20:11:24 debian12-xfs-reflink-16k-4ks kernel: huge_memory: split file-backed THPs in file: /media/scratch/test/p0/dc/dd/d274/d2ca/de12/d139/d4b1/d3cf/d4bb/d1240/d96c/d902/d7a5/d8b0/dbfb/dd18/d795/d8a1/dcc5/d1950/d19ed/d1204/d1452/db5f/dbb7/d10e8/d316/d707/f8f3, page offset: [0x0 - 0x17c0000] with order: 2
Apr 28 20:11:24 debian12-xfs-reflink-16k-4ks kernel: huge_memory: 0 of 6 file-backed THP split
Apr 28 20:11:24 debian12-xfs-reflink-16k-4ks kernel: huge_memory: split file-backed THPs in file: /media/scratch/test/p0/dc/dd/d274/d2ca/de12/d139/d4b1/d3cf/d4bb/d1240/d96c/d902/d7a5/d8b0/dbfb/dd18/d795/d8a1/dcc5/d1950/d19ed/d1204/d1452/db5f/dbb7/d10e8/d316/d707/fbb8, page offset: [0x0 - 0x32b533] with order: 2
Apr 28 20:11:24 debian12-xfs-reflink-16k-4ks kernel: huge_memory: 0 of 5 file-backed THP split
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: BUG: kernel NULL pointer dereference, address: 0000000000000000
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: #PF: supervisor read access in kernel mode
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: #PF: error_code(0x0000) - not-present page
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: PGD 0 P4D 0
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: Oops: 0000 [#1] PREEMPT SMP NOPTI
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: CPU: 7 PID: 2177 Comm: 745 Not tainted 6.9.0-rc5+ #5
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: RIP: 0010:vsscanf (lib/vsprintf.c:3465)
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: Code: 0f 85 1d 02 00 00 48 8b 54 24 08 0f b6 02 3c 25 40 0f 95 c7 84 c0 0f 95 c1 40 20 cf 41 89 fe 74 40 48 8d 4a 01 48 89 4c 24 08 <41> 0f b6 45 00 38 02 0f 84 87 02 00 00 48 8b 44 24 38 65 48 2b 04
All code
========
0: 0f 85 1d 02 00 00 jne 0x223
6: 48 8b 54 24 08 mov 0x8(%rsp),%rdx
b: 0f b6 02 movzbl (%rdx),%eax
e: 3c 25 cmp $0x25,%al
10: 40 0f 95 c7 setne %dil
14: 84 c0 test %al,%al
16: 0f 95 c1 setne %cl
19: 40 20 cf and %cl,%dil
1c: 41 89 fe mov %edi,%r14d
1f: 74 40 je 0x61
21: 48 8d 4a 01 lea 0x1(%rdx),%rcx
25: 48 89 4c 24 08 mov %rcx,0x8(%rsp)
2a:* 41 0f b6 45 00 movzbl 0x0(%r13),%eax <-- trapping instruction
2f: 38 02 cmp %al,(%rdx)
31: 0f 84 87 02 00 00 je 0x2be
37: 48 8b 44 24 38 mov 0x38(%rsp),%rax
3c: 65 gs
3d: 48 rex.W
3e: 2b .byte 0x2b
3f: 04 .byte 0x4

Code starting with the faulting instruction
===========================================
0: 41 0f b6 45 00 movzbl 0x0(%r13),%eax
5: 38 02 cmp %al,(%rdx)
7: 0f 84 87 02 00 00 je 0x294
d: 48 8b 44 24 38 mov 0x38(%rsp),%rax
12: 65 gs
13: 48 rex.W
14: 2b .byte 0x2b
15: 04 .byte 0x4
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: RSP: 0018:ffffb24ec358bad8 EFLAGS: 00010202
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: RAX: 0000000000000030 RBX: ffffb24ec358bb50 RCX: ffffffffa03fbc18
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: RDX: ffffffffa03fbc17 RSI: ffffffffa03fbc17 RDI: 0000000000000001
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: RBP: 0000000000000000 R08: ffffb24ec358bbdc R09: 000000000000002c
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: R10: ffffb24ec358bbfa R11: 0000000000000000 R12: 0000000000000000
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: R13: 0000000000000000 R14: 0000000000000001 R15: ffffb24ec358bf08
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: FS: 00007f8b39189740(0000) GS:ffff88837bdc0000(0000) knlGS:0000000000000000
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: CR2: 0000000000000000 CR3: 000000010c9f2003 CR4: 0000000000770ef0
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: DR3: 0000000000000000 DR6: 00000000fffe07f0 DR7: 0000000000000400
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: PKRU: 55555554
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: Call Trace:
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: <TASK>
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: ? __die (arch/x86/kernel/dumpstack.c:421 arch/x86/kernel/dumpstack.c:434)
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: ? page_fault_oops (arch/x86/mm/fault.c:713)
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: ? do_user_addr_fault (./include/linux/kprobes.h:591 (discriminator 1) arch/x86/mm/fault.c:1265 (discriminator 1))
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: ? exc_page_fault (./arch/x86/include/asm/paravirt.h:693 arch/x86/mm/fault.c:1513 arch/x86/mm/fault.c:1563)
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: ? asm_exc_page_fault (./arch/x86/include/asm/idtentry.h:623)
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: ? vsscanf (lib/vsprintf.c:3465)
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: ? stack_depot_save_flags (lib/stackdepot.c:609)
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: sscanf (lib/vsprintf.c:3725)
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: ? __check_object_size (mm/usercopy.c:226 (discriminator 1) mm/usercopy.c:213 (discriminator 1))
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: split_huge_pages_write (mm/huge_memory.c:3664)
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: full_proxy_write (fs/debugfs/file.c:328 (discriminator 1))
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: vfs_write (fs/read_write.c:588)
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: ? __count_memcg_events (mm/memcontrol.c:723 (discriminator 1) mm/memcontrol.c:962 (discriminator 1))
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: ? count_memcg_events.constprop.0 (./arch/x86/include/asm/irqflags.h:134 (discriminator 1) ./include/linux/memcontrol.h:1097 (discriminator 1))
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: ? handle_mm_fault (mm/memory.c:5483 mm/memory.c:5622)
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: ? preempt_count_add (./include/linux/ftrace.h:974 (discriminator 1) kernel/sched/core.c:5852 (discriminator 1) kernel/sched/core.c:5849 (discriminator 1) kernel/sched/core.c:5877 (discriminator 1))
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: ksys_write (fs/read_write.c:643)
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: do_syscall_64 (arch/x86/entry/common.c:52 (discriminator 1) arch/x86/entry/common.c:83 (discriminator 1))
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: RIP: 0033:0x7f8b39284240
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: Code: 40 00 48 8b 15 c1 9b 0d 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b7 0f 1f 00 80 3d a1 23 0e 00 00 74 17 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 58 c3 0f 1f 80 00 00 00 00 48 83 ec 28 48 89
All code
========
0: 40 00 48 8b rex add %cl,-0x75(%rax)
4: 15 c1 9b 0d 00 adc $0xd9bc1,%eax
9: f7 d8 neg %eax
b: 64 89 02 mov %eax,%fs:(%rdx)
e: 48 c7 c0 ff ff ff ff mov $0xffffffffffffffff,%rax
15: eb b7 jmp 0xffffffffffffffce
17: 0f 1f 00 nopl (%rax)
1a: 80 3d a1 23 0e 00 00 cmpb $0x0,0xe23a1(%rip) # 0xe23c2
21: 74 17 je 0x3a
23: b8 01 00 00 00 mov $0x1,%eax
28: 0f 05 syscall
2a:* 48 3d 00 f0 ff ff cmp $0xfffffffffffff000,%rax <-- trapping instruction
30: 77 58 ja 0x8a
32: c3 ret
33: 0f 1f 80 00 00 00 00 nopl 0x0(%rax)
3a: 48 83 ec 28 sub $0x28,%rsp
3e: 48 rex.W
3f: 89 .byte 0x89

Code starting with the faulting instruction
===========================================
0: 48 3d 00 f0 ff ff cmp $0xfffffffffffff000,%rax
6: 77 58 ja 0x60
8: c3 ret
9: 0f 1f 80 00 00 00 00 nopl 0x0(%rax)
10: 48 83 ec 28 sub $0x28,%rsp
14: 48 rex.W
15: 89 .byte 0x89
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: RSP: 002b:00007fff2a14b5f8 EFLAGS: 00000202 ORIG_RAX: 0000000000000001
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: RAX: ffffffffffffffda RBX: 0000000000000109 RCX: 00007f8b39284240
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: RDX: 0000000000000109 RSI: 00005589ea673400 RDI: 0000000000000001
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: RBP: 00005589ea673400 R08: 0000000000000007 R09: 0000000000000073
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000109
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: R13: 00007f8b3935f760 R14: 0000000000000109 R15: 00007f8b3935a9e0
Apr 28 20:11:25 debian12-xfs-reflink-16k-4ks kernel: </TASK>
Re: [PATCH 1/2] mm/huge_memory: skip invalid debugfs file entry for folio split [ In reply to ]
akpm at linux-foundation
Apr 29, 2024, 9:23 AM
Post #6 of 6 (6 views)
Permalink
On Sun, 28 Apr 2024 21:04:50 -0700 Luis Chamberlain <mcgrof@kernel.org> wrote:

> On Thu, Apr 25, 2024 at 02:01:26PM -0700, Andrew Morton wrote:
> > On Wed, 24 Apr 2024 15:54:48 -0700 Luis Chamberlain <mcgrof@kernel.org> wrote:
> >
> > > If the file entry is too long we may easily end up going out of bounds
> > > and crash after strsep() on sscanf().
> > >
> >
> > Can you explain why? I'm not seeing it.
>
> I couldn't see it either but I just looked at the crash below and
> its the only thing I could think of. So I think its when userspace
> somehow abuses MAX_INPUT_BUF_SZ a lot somehow.

This isn't a good basis for making kernel changes :(

Can you investigate a little further please? What actually is present
at *buf when your new checks succeed? Could we be seeing 0xNNN,0xNNN
and leaving new_order unaltered? Or something.

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