255 lines
6.8 KiB
C
255 lines
6.8 KiB
C
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/*
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* Access kernel memory without faulting.
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*/
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#include <linux/export.h>
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#include <linux/mm.h>
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#include <linux/uaccess.h>
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static __always_inline long
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probe_read_common(void *dst, const void __user *src, size_t size)
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{
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long ret;
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pagefault_disable();
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ret = __copy_from_user_inatomic(dst, src, size);
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pagefault_enable();
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return ret ? -EFAULT : 0;
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}
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static __always_inline long
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probe_write_common(void __user *dst, const void *src, size_t size)
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{
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long ret;
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pagefault_disable();
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ret = __copy_to_user_inatomic(dst, src, size);
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pagefault_enable();
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return ret ? -EFAULT : 0;
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}
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/**
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* probe_kernel_read(): safely attempt to read from a kernel-space location
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* @dst: pointer to the buffer that shall take the data
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* @src: address to read from
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* @size: size of the data chunk
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*
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* Safely read from address @src to the buffer at @dst. If a kernel fault
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* happens, handle that and return -EFAULT.
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*
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* We ensure that the copy_from_user is executed in atomic context so that
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* do_page_fault() doesn't attempt to take mmap_sem. This makes
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* probe_kernel_read() suitable for use within regions where the caller
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* already holds mmap_sem, or other locks which nest inside mmap_sem.
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*/
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long __weak probe_kernel_read(void *dst, const void *src, size_t size)
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__attribute__((alias("__probe_kernel_read")));
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long __probe_kernel_read(void *dst, const void *src, size_t size)
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{
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long ret;
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mm_segment_t old_fs = get_fs();
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set_fs(KERNEL_DS);
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ret = probe_read_common(dst, (__force const void __user *)src, size);
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set_fs(old_fs);
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return ret;
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}
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EXPORT_SYMBOL_GPL(probe_kernel_read);
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/**
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* probe_user_read(): safely attempt to read from a user-space location
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* @dst: pointer to the buffer that shall take the data
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* @src: address to read from. This must be a user address.
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* @size: size of the data chunk
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*
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* Safely read from user address @src to the buffer at @dst. If a kernel fault
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* happens, handle that and return -EFAULT.
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*/
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long __weak probe_user_read(void *dst, const void __user *src, size_t size)
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__attribute__((alias("__probe_user_read")));
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long __probe_user_read(void *dst, const void __user *src, size_t size)
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{
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long ret = -EFAULT;
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mm_segment_t old_fs = get_fs();
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set_fs(USER_DS);
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if (access_ok(VERIFY_READ, src, size))
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ret = probe_read_common(dst, src, size);
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set_fs(old_fs);
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return ret;
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}
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EXPORT_SYMBOL_GPL(probe_user_read);
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/**
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* probe_kernel_write(): safely attempt to write to a location
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* @dst: address to write to
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* @src: pointer to the data that shall be written
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* @size: size of the data chunk
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*
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* Safely write to address @dst from the buffer at @src. If a kernel fault
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* happens, handle that and return -EFAULT.
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*/
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long __weak probe_kernel_write(void *dst, const void *src, size_t size)
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__attribute__((alias("__probe_kernel_write")));
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long __probe_kernel_write(void *dst, const void *src, size_t size)
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{
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long ret;
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mm_segment_t old_fs = get_fs();
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set_fs(KERNEL_DS);
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ret = probe_write_common((__force void __user *)dst, src, size);
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set_fs(old_fs);
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return ret;
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}
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EXPORT_SYMBOL_GPL(probe_kernel_write);
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/**
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* probe_user_write(): safely attempt to write to a user-space location
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* @dst: address to write to
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* @src: pointer to the data that shall be written
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* @size: size of the data chunk
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*
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* Safely write to address @dst from the buffer at @src. If a kernel fault
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* happens, handle that and return -EFAULT.
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*/
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long __weak probe_user_write(void __user *dst, const void *src, size_t size)
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__attribute__((alias("__probe_user_write")));
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long __probe_user_write(void __user *dst, const void *src, size_t size)
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{
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long ret = -EFAULT;
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mm_segment_t old_fs = get_fs();
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set_fs(USER_DS);
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if (access_ok(VERIFY_WRITE, dst, size))
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ret = probe_write_common(dst, src, size);
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set_fs(old_fs);
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return ret;
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}
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EXPORT_SYMBOL_GPL(probe_user_write);
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/**
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* strncpy_from_unsafe: - Copy a NUL terminated string from unsafe address.
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* @dst: Destination address, in kernel space. This buffer must be at
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* least @count bytes long.
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* @src: Unsafe address.
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* @count: Maximum number of bytes to copy, including the trailing NUL.
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*
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* Copies a NUL-terminated string from unsafe address to kernel buffer.
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*
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* On success, returns the length of the string INCLUDING the trailing NUL.
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*
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* If access fails, returns -EFAULT (some data may have been copied
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* and the trailing NUL added).
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*
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* If @count is smaller than the length of the string, copies @count-1 bytes,
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* sets the last byte of @dst buffer to NUL and returns @count.
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*/
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long strncpy_from_unsafe(char *dst, const void *unsafe_addr, long count)
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{
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mm_segment_t old_fs = get_fs();
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const void *src = unsafe_addr;
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long ret;
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if (unlikely(count <= 0))
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return 0;
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set_fs(KERNEL_DS);
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pagefault_disable();
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do {
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ret = __get_user(*dst++, (const char __user __force *)src++);
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} while (dst[-1] && ret == 0 && src - unsafe_addr < count);
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dst[-1] = '\0';
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pagefault_enable();
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set_fs(old_fs);
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return ret ? -EFAULT : src - unsafe_addr;
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}
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/**
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* strncpy_from_unsafe_user: - Copy a NUL terminated string from unsafe user
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* address.
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* @dst: Destination address, in kernel space. This buffer must be at
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* least @count bytes long.
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* @unsafe_addr: Unsafe user address.
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* @count: Maximum number of bytes to copy, including the trailing NUL.
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*
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* Copies a NUL-terminated string from unsafe user address to kernel buffer.
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*
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* On success, returns the length of the string INCLUDING the trailing NUL.
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*
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* If access fails, returns -EFAULT (some data may have been copied
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* and the trailing NUL added).
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*
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* If @count is smaller than the length of the string, copies @count-1 bytes,
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* sets the last byte of @dst buffer to NUL and returns @count.
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*/
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long strncpy_from_unsafe_user(char *dst, const void __user *unsafe_addr,
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long count)
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{
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mm_segment_t old_fs = get_fs();
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long ret;
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if (unlikely(count <= 0))
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return 0;
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set_fs(USER_DS);
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pagefault_disable();
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ret = strncpy_from_user(dst, unsafe_addr, count);
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pagefault_enable();
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set_fs(old_fs);
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if (ret >= count) {
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ret = count;
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dst[ret - 1] = '\0';
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} else if (ret > 0) {
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ret++;
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}
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return ret;
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}
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/**
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* strnlen_unsafe_user: - Get the size of a user string INCLUDING final NUL.
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* @unsafe_addr: The string to measure.
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* @count: Maximum count (including NUL)
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*
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* Get the size of a NUL-terminated string in user space without pagefault.
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*
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* Returns the size of the string INCLUDING the terminating NUL.
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*
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* If the string is too long, returns a number larger than @count. User
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* has to check the return value against "> count".
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* On exception (or invalid count), returns 0.
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*
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* Unlike strnlen_user, this can be used from IRQ handler etc. because
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* it disables pagefaults.
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*/
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long strnlen_unsafe_user(const void __user *unsafe_addr, long count)
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{
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mm_segment_t old_fs = get_fs();
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int ret;
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set_fs(USER_DS);
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pagefault_disable();
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ret = strnlen_user(unsafe_addr, count);
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pagefault_enable();
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set_fs(old_fs);
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return ret;
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}
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