On Mon, Feb 25, 2019 at 11:05:41PM +0900, Masami Hiramatsu wrote:
> +static __always_inline long __strncpy_from_unsafe_user(char *dst,
> + const char __user *unsafe_addr, long count)
> +{
> + if (!access_ok(unsafe_addr, count))
> + return -EFAULT;
> +
> + return strncpy_from_unsafe_common(dst, unsafe_addr, count);
> +}
Would something like so work for people?
---
arch/x86/include/asm/uaccess.h | 8 +++++++-
include/linux/uaccess.h | 18 ++++++++++++++++++
2 files changed, 25 insertions(+), 1 deletion(-)
diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index 780f2b42c8ef..3125d129d3b6 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -92,12 +92,18 @@ static inline bool __chk_range_not_ok(unsigned long addr,
unsigned long size, un
* checks that the pointer is in the user space range - after calling
* this function, memory access functions may still return -EFAULT.
*/
-#define access_ok(addr, size) \
+#define access_ok(addr, size) \
({ \
WARN_ON_IN_IRQ(); \
likely(!__range_not_ok(addr, size, user_addr_max())); \
})
+#define user_access_ok(addr, size) \
+({ \
+ WARN_ON_ONCE(!segment_eq(get_fs(), USER_DS)); \
+ likely(!__range_not_ok(addr, size, user_addr_max())); \
+})
+
/*
* These are the main single-value transfer routines. They automatically
* use the right size if we just have the right pointer type.
diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
index 37b226e8df13..088f2ae09e14 100644
--- a/include/linux/uaccess.h
+++ b/include/linux/uaccess.h
@@ -10,6 +10,24 @@
#include <asm/uaccess.h>
+/**
+ * user_access_ok: Checks if a user space pointer is valid
+ * @addr: User space pointer to start of block to check
+ * @size: Size of block to check
+ *
+ * Context: User context or explicit set_fs(USER_DS).
+ *
+ * This function is very much like access_ok(), except it (may) have different
+ * context validation. In general we must be very careful when using this.
+ */
+#ifndef user_access_ok
+#define user_access_ok(addr, size) \
+({ \
+ WARN_ON_ONCE(!segment_eq(get_fs(), USER_DS)); \
+ access_ok(addr, size); \
+})
+#endif
+
/*
* Architectures should provide two primitives (raw_copy_{to,from}_user())
* and get rid of their private instances of copy_{to,from}_user() and
> +/**
> + * strncpy_from_unsafe_user: - Copy a NUL terminated string from unsafe user
> + * address.
> + * @dst: Destination address, in kernel space. This buffer must be at
> + * least @count bytes long.
> + * @unsafe_addr: Unsafe user address.
> + * @count: Maximum number of bytes to copy, including the trailing NUL.
> + *
> + * Copies a NUL-terminated string from unsafe user address to kernel buffer.
> + *
> + * On success, returns the length of the string INCLUDING the trailing NUL.
> + *
> + * If access fails, returns -EFAULT (some data may have been copied
> + * and the trailing NUL added).
> + *
> + * If @count is smaller than the length of the string, copies @count-1 bytes,
> + * sets the last byte of @dst buffer to NUL and returns @count.
> + */
> +long strncpy_from_unsafe_user(char *dst, const void __user *unsafe_addr,
> + long count)
> +{
> + mm_segment_t old_fs = get_fs();
> + long ret;
> +
> + if (unlikely(count <= 0))
> + return 0;
> +
> + if (segment_eq(old_fs, USER_DS)) {
> + ret = __strncpy_from_unsafe_user(dst, unsafe_addr, count);
> + } else {
> + set_fs(USER_DS);
> + ret = __strncpy_from_unsafe_user(dst, unsafe_addr, count);
> + set_fs(old_fs);
> + }
> + return ret;
> }
Is that really worth the effort?
Why not keep it simple:
mm_segment_t old_fs = get_fs();
set_fs(USER_DS);
ret = __strncpy...();
set_fs(old_fd);
return ret;
?
