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authorLinus Torvalds <torvalds@linux-foundation.org>2012-05-26 16:57:16 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2012-05-26 16:57:16 -0700
commit1e2aec873ad6d16538512dbb96853caa1fa076af (patch)
treed792b19ac47be44debd24610ae27f1330fa490e4 /lib/strnlen_user.c
parentae32adc1e06d096399f195eeda12d443d53539c4 (diff)
parent2c66f623631709aa5f2e4c14c7e089682e7394a3 (diff)
downloadlinux-1e2aec873ad6d16538512dbb96853caa1fa076af.tar.bz2
Merge branch 'generic-string-functions'
This makes <asm/word-at-a-time.h> actually live up to its promise of allowing architectures to help tune the string functions that do their work a word at a time. David had already taken the x86 strncpy_from_user() function, modified it to work on sparc, and then done the extra work to make it generically useful. This then expands on that work by making x86 use that generic version, completing the circle. But more importantly, it fixes up the word-at-a-time interfaces so that it's now easy to also support things like strnlen_user(), and pretty much most random string functions. David reports that it all works fine on sparc, and Jonas Bonn reported that an earlier version of this worked on OpenRISC too. It's pretty easy for architectures to add support for this and just replace their private versions with the generic code. * generic-string-functions: sparc: use the new generic strnlen_user() function x86: use the new generic strnlen_user() function lib: add generic strnlen_user() function word-at-a-time: make the interfaces truly generic x86: use generic strncpy_from_user routine
Diffstat (limited to 'lib/strnlen_user.c')
-rw-r--r--lib/strnlen_user.c138
1 files changed, 138 insertions, 0 deletions
diff --git a/lib/strnlen_user.c b/lib/strnlen_user.c
new file mode 100644
index 000000000000..90900ecfeb54
--- /dev/null
+++ b/lib/strnlen_user.c
@@ -0,0 +1,138 @@
+#include <linux/kernel.h>
+#include <linux/export.h>
+#include <linux/uaccess.h>
+
+#include <asm/word-at-a-time.h>
+
+/* Set bits in the first 'n' bytes when loaded from memory */
+#ifdef __LITTLE_ENDIAN
+# define aligned_byte_mask(n) ((1ul << 8*(n))-1)
+#else
+# define aligned_byte_mask(n) (~0xfful << 8*(7-(n)))
+#endif
+
+/*
+ * Do a strnlen, return length of string *with* final '\0'.
+ * 'count' is the user-supplied count, while 'max' is the
+ * address space maximum.
+ *
+ * Return 0 for exceptions (which includes hitting the address
+ * space maximum), or 'count+1' if hitting the user-supplied
+ * maximum count.
+ *
+ * NOTE! We can sometimes overshoot the user-supplied maximum
+ * if it fits in a aligned 'long'. The caller needs to check
+ * the return value against "> max".
+ */
+static inline long do_strnlen_user(const char __user *src, unsigned long count, unsigned long max)
+{
+ const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
+ long align, res = 0;
+ unsigned long c;
+
+ /*
+ * Truncate 'max' to the user-specified limit, so that
+ * we only have one limit we need to check in the loop
+ */
+ if (max > count)
+ max = count;
+
+ /*
+ * Do everything aligned. But that means that we
+ * need to also expand the maximum..
+ */
+ align = (sizeof(long) - 1) & (unsigned long)src;
+ src -= align;
+ max += align;
+
+ if (unlikely(__get_user(c,(unsigned long __user *)src)))
+ return 0;
+ c |= aligned_byte_mask(align);
+
+ for (;;) {
+ unsigned long data;
+ if (has_zero(c, &data, &constants)) {
+ data = prep_zero_mask(c, data, &constants);
+ data = create_zero_mask(data);
+ return res + find_zero(data) + 1 - align;
+ }
+ res += sizeof(unsigned long);
+ if (unlikely(max < sizeof(unsigned long)))
+ break;
+ max -= sizeof(unsigned long);
+ if (unlikely(__get_user(c,(unsigned long __user *)(src+res))))
+ return 0;
+ }
+ res -= align;
+
+ /*
+ * Uhhuh. We hit 'max'. But was that the user-specified maximum
+ * too? If so, return the marker for "too long".
+ */
+ if (res >= count)
+ return count+1;
+
+ /*
+ * Nope: we hit the address space limit, and we still had more
+ * characters the caller would have wanted. That's 0.
+ */
+ return 0;
+}
+
+/**
+ * strnlen_user: - Get the size of a user string INCLUDING final NUL.
+ * @str: The string to measure.
+ * @count: Maximum count (including NUL character)
+ *
+ * Context: User context only. This function may sleep.
+ *
+ * Get the size of a NUL-terminated string in user space.
+ *
+ * Returns the size of the string INCLUDING the terminating NUL.
+ * If the string is too long, returns 'count+1'.
+ * On exception (or invalid count), returns 0.
+ */
+long strnlen_user(const char __user *str, long count)
+{
+ unsigned long max_addr, src_addr;
+
+ if (unlikely(count <= 0))
+ return 0;
+
+ max_addr = user_addr_max();
+ src_addr = (unsigned long)str;
+ if (likely(src_addr < max_addr)) {
+ unsigned long max = max_addr - src_addr;
+ return do_strnlen_user(str, count, max);
+ }
+ return 0;
+}
+EXPORT_SYMBOL(strnlen_user);
+
+/**
+ * strlen_user: - Get the size of a user string INCLUDING final NUL.
+ * @str: The string to measure.
+ *
+ * Context: User context only. This function may sleep.
+ *
+ * Get the size of a NUL-terminated string in user space.
+ *
+ * Returns the size of the string INCLUDING the terminating NUL.
+ * On exception, returns 0.
+ *
+ * If there is a limit on the length of a valid string, you may wish to
+ * consider using strnlen_user() instead.
+ */
+long strlen_user(const char __user *str)
+{
+ unsigned long max_addr, src_addr;
+
+ max_addr = user_addr_max();
+ src_addr = (unsigned long)str;
+ if (likely(src_addr < max_addr)) {
+ unsigned long max = max_addr - src_addr;
+ return do_strnlen_user(str, ~0ul, max);
+ }
+ return 0;
+}
+EXPORT_SYMBOL(strlen_user);