[merged] exec-open-code-copy_string_kernel.patch removed from -mm tree

[merged] exec-open-code-copy_string_kernel.patch removed from -mm tree

[akpm]

The patch titled
     Subject: exec: open code copy_string_kernel
has been removed from the -mm tree.  Its filename was
     exec-open-code-copy_string_kernel.patch

This patch was dropped because it was merged into mainline or a subsystem tree

------------------------------------------------------
From: Christoph Hellwig <hch@lst.de>
Subject: exec: open code copy_string_kernel

Currently copy_string_kernel is just a wrapper around copy_strings that
simplifies the calling conventions and uses set_fs to allow passing a
kernel pointer.  But due to the fact the we only need to handle a single
kernel argument pointer, the logic can be sigificantly simplified while
getting rid of the set_fs.

Link: http://lkml.kernel.org/r/20200501104105.2621149-3-hch@lst.de
Signed-off-by: Christoph Hellwig <hch@lst.de>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 fs/exec.c |   45 +++++++++++++++++++++++++++++++++++----------
 1 file changed, 35 insertions(+), 10 deletions(-)

--- a/fs/exec.c~exec-open-code-copy_string_kernel
+++ a/fs/exec.c
@@ -592,17 +592,42 @@ out:
  */
 int copy_string_kernel(const char *arg, struct linux_binprm *bprm)
 {
-	int r;
-	mm_segment_t oldfs = get_fs();
-	struct user_arg_ptr argv = {
-		.ptr.native = (const char __user *const  __user *)&arg,
-	};
-
-	set_fs(KERNEL_DS);
-	r = copy_strings(1, argv, bprm);
-	set_fs(oldfs);
+	int len = strnlen(arg, MAX_ARG_STRLEN) + 1 /* terminating NUL */;
+	unsigned long pos = bprm->p;
 
-	return r;
+	if (len == 0)
+		return -EFAULT;
+	if (!valid_arg_len(bprm, len))
+		return -E2BIG;
+
+	/* We're going to work our way backwards. */
+	arg += len;
+	bprm->p -= len;
+	if (IS_ENABLED(CONFIG_MMU) && bprm->p < bprm->argmin)
+		return -E2BIG;
+
+	while (len > 0) {
+		unsigned int bytes_to_copy = min_t(unsigned int, len,
+				min_not_zero(offset_in_page(pos), PAGE_SIZE));
+		struct page *page;
+		char *kaddr;
+
+		pos -= bytes_to_copy;
+		arg -= bytes_to_copy;
+		len -= bytes_to_copy;
+
+		page = get_arg_page(bprm, pos, 1);
+		if (!page)
+			return -E2BIG;
+		kaddr = kmap_atomic(page);
+		flush_arg_page(bprm, pos & PAGE_MASK, page);
+		memcpy(kaddr + offset_in_page(pos), arg, bytes_to_copy);
+		flush_kernel_dcache_page(page);
+		kunmap_atomic(kaddr);
+		put_arg_page(page);
+	}
+
+	return 0;
 }
 EXPORT_SYMBOL(copy_string_kernel);
 
_

Patches currently in -mm which might be from hch@lst.de are

amdgpu-a-null-mm-does-not-mean-a-thread-is-a-kthread.patch
kernel-move-use_mm-unuse_mm-to-kthreadc.patch
kernel-move-use_mm-unuse_mm-to-kthreadc-v2.patch
kernel-better-document-the-use_mm-unuse_mm-api-contract.patch
kernel-better-document-the-use_mm-unuse_mm-api-contract-v2.patch
kernel-set-user_ds-in-kthread_use_mm.patch
arm-fix-the-flush_icache_range-arguments-in-set_fiq_handler.patch
nds32-unexport-flush_icache_page.patch
powerpc-unexport-flush_icache_user_range.patch
unicore32-remove-flush_cache_user_range.patch
asm-generic-fix-the-inclusion-guards-for-cacheflushh.patch
asm-generic-dont-include-linux-mmh-in-cacheflushh.patch
asm-generic-dont-include-linux-mmh-in-cacheflushh-fix.patch
asm-generic-improve-the-flush_dcache_page-stub.patch
alpha-use-asm-generic-cacheflushh.patch
arm64-use-asm-generic-cacheflushh.patch
c6x-use-asm-generic-cacheflushh.patch
hexagon-use-asm-generic-cacheflushh.patch
ia64-use-asm-generic-cacheflushh.patch
microblaze-use-asm-generic-cacheflushh.patch
m68knommu-use-asm-generic-cacheflushh.patch
openrisc-use-asm-generic-cacheflushh.patch
powerpc-use-asm-generic-cacheflushh.patch
riscv-use-asm-generic-cacheflushh.patch
armsparcunicore32-remove-flush_icache_user_range.patch
mm-rename-flush_icache_user_range-to-flush_icache_user_page.patch
asm-generic-add-a-flush_icache_user_range-stub.patch
sh-implement-flush_icache_user_range.patch
xtensa-implement-flush_icache_user_range.patch
arm-rename-flush_cache_user_range-to-flush_icache_user_range.patch
m68k-implement-flush_icache_user_range.patch
exec-only-build-read_code-when-needed.patch
exec-use-flush_icache_user_range-in-read_code.patch
binfmt_flat-use-flush_icache_user_range.patch
nommu-use-flush_icache_user_range-in-brk-and-mmap.patch
module-move-the-set_fs-hack-for-flush_icache_range-to-m68k.patch
maccess-unexport-probe_kernel_write-and-probe_user_write.patch
maccess-remove-various-unused-weak-aliases.patch
maccess-remove-duplicate-kerneldoc-comments.patch
maccess-clarify-kerneldoc-comments.patch
maccess-update-the-top-of-file-comment.patch
maccess-rename-strncpy_from_unsafe_user-to-strncpy_from_user_nofault.patch
maccess-rename-strncpy_from_unsafe_strict-to-strncpy_from_kernel_nofault.patch
maccess-rename-strnlen_unsafe_user-to-strnlen_user_nofault.patch
maccess-remove-probe_read_common-and-probe_write_common.patch
maccess-unify-the-probe-kernel-arch-hooks.patch
bpf-factor-out-a-bpf_trace_copy_string-helper.patch
bpf-handle-the-compat-string-in-bpf_trace_copy_string-better.patch
bpf-rework-the-compat-kernel-probe-handling.patch
tracing-kprobes-handle-mixed-kernel-userspace-probes-better.patch
maccess-remove-strncpy_from_unsafe.patch
maccess-always-use-strict-semantics-for-probe_kernel_read.patch
maccess-move-user-access-routines-together.patch
maccess-allow-architectures-to-provide-kernel-probing-directly.patch
x86-use-non-set_fs-based-maccess-routines.patch
maccess-return-erange-when-copy_from_kernel_nofault_allowed-fails.patch

Re: [merged] exec-open-code-copy_string_kernel.patch removed from -mm tree

[Vegard Nossum]

On 2020-06-05 22:19, akpm@linux-foundation.org wrote:
> The patch titled
>       Subject: exec: open code copy_string_kernel
> has been removed from the -mm tree.  Its filename was
>       exec-open-code-copy_string_kernel.patch
> 
> This patch was dropped because it was merged into mainline or a subsystem tree
> 
> ------------------------------------------------------
> From: Christoph Hellwig <hch@lst.de>
> Subject: exec: open code copy_string_kernel
> 
> Currently copy_string_kernel is just a wrapper around copy_strings that
> simplifies the calling conventions and uses set_fs to allow passing a
> kernel pointer.  But due to the fact the we only need to handle a single
> kernel argument pointer, the logic can be sigificantly simplified while
> getting rid of the set_fs.
> 
> Link: http://lkml.kernel.org/r/20200501104105.2621149-3-hch@lst.de
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> Cc: Alexander Viro <viro@zeniv.linux.org.uk>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> ---
> 
>   fs/exec.c |   45 +++++++++++++++++++++++++++++++++++----------
>   1 file changed, 35 insertions(+), 10 deletions(-)
> 
> --- a/fs/exec.c~exec-open-code-copy_string_kernel
> +++ a/fs/exec.c
> @@ -592,17 +592,42 @@ out:
>    */
>   int copy_string_kernel(const char *arg, struct linux_binprm *bprm)
>   {
> -	int r;
> -	mm_segment_t oldfs = get_fs();
> -	struct user_arg_ptr argv = {
> -		.ptr.native = (const char __user *const  __user *)&arg,
> -	};
> -
> -	set_fs(KERNEL_DS);
> -	r = copy_strings(1, argv, bprm);
> -	set_fs(oldfs);
> +	int len = strnlen(arg, MAX_ARG_STRLEN) + 1 /* terminating NUL */;
> +	unsigned long pos = bprm->p;
>   
> -	return r;
> +	if (len == 0)
> +		return -EFAULT;

Just a quick question, how can len ever be 0 here when len was set to
strnlen() + 1? Should the test be different?

The old version (i.e. copy_strings()) seems to return -EFAULT when
strnlen() returns 0.


Vegard

> +	if (!valid_arg_len(bprm, len))
> +		return -E2BIG;
> +
> +	/* We're going to work our way backwards. */
> +	arg += len;
> +	bprm->p -= len;
> +	if (IS_ENABLED(CONFIG_MMU) && bprm->p < bprm->argmin)
> +		return -E2BIG;
> +
> +	while (len > 0) {
> +		unsigned int bytes_to_copy = min_t(unsigned int, len,
> +				min_not_zero(offset_in_page(pos), PAGE_SIZE));
> +		struct page *page;
> +		char *kaddr;
> +
> +		pos -= bytes_to_copy;
> +		arg -= bytes_to_copy;
> +		len -= bytes_to_copy;
> +
> +		page = get_arg_page(bprm, pos, 1);
> +		if (!page)
> +			return -E2BIG;
> +		kaddr = kmap_atomic(page);
> +		flush_arg_page(bprm, pos & PAGE_MASK, page);
> +		memcpy(kaddr + offset_in_page(pos), arg, bytes_to_copy);
> +		flush_kernel_dcache_page(page);
> +		kunmap_atomic(kaddr);
> +		put_arg_page(page);
> +	}
> +
> +	return 0;
>   }
>   EXPORT_SYMBOL(copy_string_kernel);
>   

Re: [merged] exec-open-code-copy_string_kernel.patch removed from -mm tree

[Christoph Hellwig]

On Tue, Jun 16, 2020 at 03:14:44PM +0200, Vegard Nossum wrote:
>
> On 2020-06-05 22:19, akpm@linux-foundation.org wrote:
>> The patch titled
>>       Subject: exec: open code copy_string_kernel
>> has been removed from the -mm tree.  Its filename was
>>       exec-open-code-copy_string_kernel.patch
>>
>> This patch was dropped because it was merged into mainline or a subsystem tree
>>
>> ------------------------------------------------------
>> From: Christoph Hellwig <hch@lst.de>
>> Subject: exec: open code copy_string_kernel
>>
>> Currently copy_string_kernel is just a wrapper around copy_strings that
>> simplifies the calling conventions and uses set_fs to allow passing a
>> kernel pointer.  But due to the fact the we only need to handle a single
>> kernel argument pointer, the logic can be sigificantly simplified while
>> getting rid of the set_fs.
>>
>> Link: http://lkml.kernel.org/r/20200501104105.2621149-3-hch@lst.de
>> Signed-off-by: Christoph Hellwig <hch@lst.de>
>> Cc: Alexander Viro <viro@zeniv.linux.org.uk>
>> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
>> ---
>>
>>   fs/exec.c |   45 +++++++++++++++++++++++++++++++++++----------
>>   1 file changed, 35 insertions(+), 10 deletions(-)
>>
>> --- a/fs/exec.c~exec-open-code-copy_string_kernel
>> +++ a/fs/exec.c
>> @@ -592,17 +592,42 @@ out:
>>    */
>>   int copy_string_kernel(const char *arg, struct linux_binprm *bprm)
>>   {
>> -	int r;
>> -	mm_segment_t oldfs = get_fs();
>> -	struct user_arg_ptr argv = {
>> -		.ptr.native = (const char __user *const  __user *)&arg,
>> -	};
>> -
>> -	set_fs(KERNEL_DS);
>> -	r = copy_strings(1, argv, bprm);
>> -	set_fs(oldfs);
>> +	int len = strnlen(arg, MAX_ARG_STRLEN) + 1 /* terminating NUL */;
>> +	unsigned long pos = bprm->p;
>>   -	return r;
>> +	if (len == 0)
>> +		return -EFAULT;
>
> Just a quick question, how can len ever be 0 here when len was set to
> strnlen() + 1? Should the test be different?
>
> The old version (i.e. copy_strings()) seems to return -EFAULT when
> strnlen() returns 0.

So, the nasty part here is that strnlen_user has different semantics
from strnlen:

 - strlen excludes the terminating null byte and never returns error
   codes
 - strnlen_user includes the terminating null byte, and a 0 return
   means it could not access the user address (a condition that can't
   happen for strlen).

Now with that back to your original question:  I think then len == 0
check can just be removed without replacement.