diff options
Diffstat (limited to 'lib')
| -rw-r--r-- | lib/Kconfig | 3 | ||||
| -rw-r--r-- | lib/Makefile | 1 | ||||
| -rw-r--r-- | lib/strnlen_user.c | 138 |
3 files changed, 142 insertions, 0 deletions
diff --git a/lib/Kconfig b/lib/Kconfig index 98230ac3db2..64ddc44d0b8 100644 --- a/lib/Kconfig +++ b/lib/Kconfig @@ -19,6 +19,9 @@ config RATIONAL config GENERIC_STRNCPY_FROM_USER bool +config GENERIC_STRNLEN_USER + bool + config GENERIC_FIND_FIRST_BIT bool diff --git a/lib/Makefile b/lib/Makefile index b98df505f33..77937a7dd5c 100644 --- a/lib/Makefile +++ b/lib/Makefile @@ -126,6 +126,7 @@ obj-$(CONFIG_CLZ_TAB) += clz_tab.o obj-$(CONFIG_DDR) += jedec_ddr_data.o obj-$(CONFIG_GENERIC_STRNCPY_FROM_USER) += strncpy_from_user.o +obj-$(CONFIG_GENERIC_STRNLEN_USER) += strnlen_user.o hostprogs-y := gen_crc32table clean-files := crc32table.h diff --git a/lib/strnlen_user.c b/lib/strnlen_user.c new file mode 100644 index 00000000000..90900ecfeb5 --- /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); |