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uaccess: Add non-pagefault user-space write function

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Commit 3d7081822f ("uaccess: Add non-pagefault user-space read functions")
missed to add probe write function, therefore factor out a probe_write_common()
helper with most logic of probe_kernel_write() except setting KERNEL_DS, and
add a new probe_user_write() helper so it can be used from BPF side.

Again, on some archs, the user address space and kernel address space can
co-exist and be overlapping, so in such case, setting KERNEL_DS would mean
that the given address is treated as being in kernel address space.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Link: https://lore.kernel.org/bpf/9df2542e68141bfa3addde631441ee45503856a8.1572649915.git.daniel@iogearbox.net
This commit is contained in:
Daniel Borkmann 2019-11-02 00:17:56 +01:00 committed by Alexei Starovoitov
parent e1cb7d2d60
commit 1d1585ca0f
2 changed files with 53 additions and 4 deletions
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12
include/linux/uaccess.h
View File

@ -337,6 +337,18 @@ extern long __probe_user_read(void *dst, const void __user *src, size_t size);
extern long notrace probe_kernel_write(void *dst, const void *src, size_t size);
extern long notrace __probe_kernel_write(void *dst, const void *src, size_t size);
/*
* probe_user_write(): safely attempt to write to a location in user space
* @dst: address to write to
* @src: pointer to the data that shall be written
* @size: size of the data chunk
*
* Safely write to address @dst from the buffer at @src. If a kernel fault
* happens, handle that and return -EFAULT.
*/
extern long notrace probe_user_write(void __user *dst, const void *src, size_t size);
extern long notrace __probe_user_write(void __user *dst, const void *src, size_t size);
extern long strncpy_from_unsafe(char *dst, const void *unsafe_addr, long count);
extern long strncpy_from_unsafe_user(char *dst, const void __user *unsafe_addr,
long count);

45
mm/maccess.c
View File

@ -18,6 +18,18 @@ probe_read_common(void *dst, const void __user *src, size_t size)
return ret ? -EFAULT : 0;
}
static __always_inline long
probe_write_common(void __user *dst, const void *src, size_t size)
{
long ret;
pagefault_disable();
ret = __copy_to_user_inatomic(dst, src, size);
pagefault_enable();
return ret ? -EFAULT : 0;
}
/**
* probe_kernel_read(): safely attempt to read from a kernel-space location
* @dst: pointer to the buffer that shall take the data
@ -85,6 +97,7 @@ EXPORT_SYMBOL_GPL(probe_user_read);
* Safely write to address @dst from the buffer at @src. If a kernel fault
* happens, handle that and return -EFAULT.
*/
long __weak probe_kernel_write(void *dst, const void *src, size_t size)
__attribute__((alias("__probe_kernel_write")));
@ -94,15 +107,39 @@ long __probe_kernel_write(void *dst, const void *src, size_t size)
mm_segment_t old_fs = get_fs();
set_fs(KERNEL_DS);
pagefault_disable();
ret = __copy_to_user_inatomic((__force void __user *)dst, src, size);
pagefault_enable();
ret = probe_write_common((__force void __user *)dst, src, size);
set_fs(old_fs);
return ret ? -EFAULT : 0;
return ret;
}
EXPORT_SYMBOL_GPL(probe_kernel_write);
/**
* probe_user_write(): safely attempt to write to a user-space location
* @dst: address to write to
* @src: pointer to the data that shall be written
* @size: size of the data chunk
*
* Safely write to address @dst from the buffer at @src. If a kernel fault
* happens, handle that and return -EFAULT.
*/
long __weak probe_user_write(void __user *dst, const void *src, size_t size)
__attribute__((alias("__probe_user_write")));
long __probe_user_write(void __user *dst, const void *src, size_t size)
{
long ret = -EFAULT;
mm_segment_t old_fs = get_fs();
set_fs(USER_DS);
if (access_ok(dst, size))
ret = probe_write_common(dst, src, size);
set_fs(old_fs);
return ret;
}
EXPORT_SYMBOL_GPL(probe_user_write);
/**
* strncpy_from_unsafe: - Copy a NUL terminated string from unsafe address.