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![Alexei Starovoitov](/assets/img/avatar_default.png)
There are several issues with copy_from_user_nofault(): - access_ok() is designed for user context only and for that reason it has WARN_ON_IN_IRQ() which triggers when bpf, kprobe, eprobe and perf on ppc are calling it from irq. - it's missing nmi_uaccess_okay() which is a nop on all architectures except x86 where it's required. The comment in arch/x86/mm/tlb.c explains the details why it's necessary. Calling copy_from_user_nofault() from bpf, [ke]probe without this check is not safe. - __copy_from_user_inatomic() under CONFIG_HARDENED_USERCOPY is calling check_object_size()->__check_object_size()->check_heap_object()->find_vmap_area()->spin_lock() which is not safe to do from bpf, [ke]probe and perf due to potential deadlock. Fix all three issues. At the end the copy_from_user_nofault() becomes equivalent to copy_from_user_nmi() from safety point of view with a difference in the return value. Reported-by: Hsin-Wei Hung <hsinweih@uci.edu> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Florian Lehner <dev@der-flo.net> Tested-by: Hsin-Wei Hung <hsinweih@uci.edu> Tested-by: Florian Lehner <dev@der-flo.net> Link: https://lore.kernel.org/r/20230410174345.4376-2-dev@der-flo.net Signed-off-by: Alexei Starovoitov <ast@kernel.org>
230 lines
5.9 KiB
C
230 lines
5.9 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* Access kernel or user 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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#include <asm/tlb.h>
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bool __weak copy_from_kernel_nofault_allowed(const void *unsafe_src,
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size_t size)
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{
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return true;
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}
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#define copy_from_kernel_nofault_loop(dst, src, len, type, err_label) \
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while (len >= sizeof(type)) { \
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__get_kernel_nofault(dst, src, type, err_label); \
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dst += sizeof(type); \
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src += sizeof(type); \
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len -= sizeof(type); \
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}
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long copy_from_kernel_nofault(void *dst, const void *src, size_t size)
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{
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unsigned long align = 0;
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if (!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS))
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align = (unsigned long)dst | (unsigned long)src;
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if (!copy_from_kernel_nofault_allowed(src, size))
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return -ERANGE;
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pagefault_disable();
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if (!(align & 7))
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copy_from_kernel_nofault_loop(dst, src, size, u64, Efault);
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if (!(align & 3))
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copy_from_kernel_nofault_loop(dst, src, size, u32, Efault);
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if (!(align & 1))
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copy_from_kernel_nofault_loop(dst, src, size, u16, Efault);
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copy_from_kernel_nofault_loop(dst, src, size, u8, Efault);
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pagefault_enable();
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return 0;
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Efault:
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pagefault_enable();
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return -EFAULT;
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}
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EXPORT_SYMBOL_GPL(copy_from_kernel_nofault);
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#define copy_to_kernel_nofault_loop(dst, src, len, type, err_label) \
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while (len >= sizeof(type)) { \
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__put_kernel_nofault(dst, src, type, err_label); \
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dst += sizeof(type); \
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src += sizeof(type); \
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len -= sizeof(type); \
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}
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long copy_to_kernel_nofault(void *dst, const void *src, size_t size)
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{
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unsigned long align = 0;
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if (!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS))
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align = (unsigned long)dst | (unsigned long)src;
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pagefault_disable();
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if (!(align & 7))
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copy_to_kernel_nofault_loop(dst, src, size, u64, Efault);
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if (!(align & 3))
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copy_to_kernel_nofault_loop(dst, src, size, u32, Efault);
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if (!(align & 1))
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copy_to_kernel_nofault_loop(dst, src, size, u16, Efault);
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copy_to_kernel_nofault_loop(dst, src, size, u8, Efault);
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pagefault_enable();
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return 0;
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Efault:
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pagefault_enable();
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return -EFAULT;
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}
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long strncpy_from_kernel_nofault(char *dst, const void *unsafe_addr, long count)
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{
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const void *src = unsafe_addr;
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if (unlikely(count <= 0))
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return 0;
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if (!copy_from_kernel_nofault_allowed(unsafe_addr, count))
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return -ERANGE;
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pagefault_disable();
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do {
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__get_kernel_nofault(dst, src, u8, Efault);
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dst++;
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src++;
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} while (dst[-1] && src - unsafe_addr < count);
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pagefault_enable();
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dst[-1] = '\0';
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return src - unsafe_addr;
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Efault:
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pagefault_enable();
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dst[0] = '\0';
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return -EFAULT;
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}
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/**
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* copy_from_user_nofault(): 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 copy_from_user_nofault(void *dst, const void __user *src, size_t size)
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{
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long ret = -EFAULT;
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if (!__access_ok(src, size))
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return ret;
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if (!nmi_uaccess_okay())
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return 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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if (ret)
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return -EFAULT;
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return 0;
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}
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EXPORT_SYMBOL_GPL(copy_from_user_nofault);
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/**
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* copy_to_user_nofault(): 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 copy_to_user_nofault(void __user *dst, const void *src, size_t size)
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{
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long ret = -EFAULT;
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if (access_ok(dst, size)) {
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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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}
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if (ret)
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return -EFAULT;
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return 0;
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}
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EXPORT_SYMBOL_GPL(copy_to_user_nofault);
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/**
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* strncpy_from_user_nofault: - 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_user_nofault(char *dst, const void __user *unsafe_addr,
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long count)
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{
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long ret;
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if (unlikely(count <= 0))
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return 0;
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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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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_user_nofault: - 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_user_nofault(const void __user *unsafe_addr, long count)
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{
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int ret;
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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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return ret;
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}
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void __copy_overflow(int size, unsigned long count)
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{
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WARN(1, "Buffer overflow detected (%d < %lu)!\n", size, count);
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}
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EXPORT_SYMBOL(__copy_overflow);
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