diff options
| -rw-r--r-- | include/linux/bitops.h | 7 | ||||
| -rw-r--r-- | include/linux/uaccess.h | 70 | ||||
| -rw-r--r-- | lib/strnlen_user.c | 8 | ||||
| -rw-r--r-- | lib/test_user_copy.c | 136 | ||||
| -rw-r--r-- | lib/usercopy.c | 55 |
5 files changed, 263 insertions, 13 deletions
diff --git a/include/linux/bitops.h b/include/linux/bitops.h index cf074bce3eb3..c94a9ff9f082 100644 --- a/include/linux/bitops.h +++ b/include/linux/bitops.h @@ -4,6 +4,13 @@ #include <asm/types.h> #include <linux/bits.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 << (BITS_PER_LONG - 8 - 8*(n))) +#endif + #define BITS_PER_TYPE(type) (sizeof(type) * BITS_PER_BYTE) #define BITS_TO_LONGS(nr) DIV_ROUND_UP(nr, BITS_PER_TYPE(long)) diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h index 70bbdc38dc37..e47d0522a1f4 100644 --- a/include/linux/uaccess.h +++ b/include/linux/uaccess.h @@ -231,6 +231,76 @@ __copy_from_user_inatomic_nocache(void *to, const void __user *from, #endif /* ARCH_HAS_NOCACHE_UACCESS */ +extern __must_check int check_zeroed_user(const void __user *from, size_t size); + +/** + * copy_struct_from_user: copy a struct from userspace + * @dst: Destination address, in kernel space. This buffer must be @ksize + * bytes long. + * @ksize: Size of @dst struct. + * @src: Source address, in userspace. + * @usize: (Alleged) size of @src struct. + * + * Copies a struct from userspace to kernel space, in a way that guarantees + * backwards-compatibility for struct syscall arguments (as long as future + * struct extensions are made such that all new fields are *appended* to the + * old struct, and zeroed-out new fields have the same meaning as the old + * struct). + * + * @ksize is just sizeof(*dst), and @usize should've been passed by userspace. + * The recommended usage is something like the following: + * + * SYSCALL_DEFINE2(foobar, const struct foo __user *, uarg, size_t, usize) + * { + * int err; + * struct foo karg = {}; + * + * if (usize > PAGE_SIZE) + * return -E2BIG; + * if (usize < FOO_SIZE_VER0) + * return -EINVAL; + * + * err = copy_struct_from_user(&karg, sizeof(karg), uarg, usize); + * if (err) + * return err; + * + * // ... + * } + * + * There are three cases to consider: + * * If @usize == @ksize, then it's copied verbatim. + * * If @usize < @ksize, then the userspace has passed an old struct to a + * newer kernel. The rest of the trailing bytes in @dst (@ksize - @usize) + * are to be zero-filled. + * * If @usize > @ksize, then the userspace has passed a new struct to an + * older kernel. The trailing bytes unknown to the kernel (@usize - @ksize) + * are checked to ensure they are zeroed, otherwise -E2BIG is returned. + * + * Returns (in all cases, some data may have been copied): + * * -E2BIG: (@usize > @ksize) and there are non-zero trailing bytes in @src. + * * -EFAULT: access to userspace failed. + */ +static __always_inline __must_check int +copy_struct_from_user(void *dst, size_t ksize, const void __user *src, + size_t usize) +{ + size_t size = min(ksize, usize); + size_t rest = max(ksize, usize) - size; + + /* Deal with trailing bytes. */ + if (usize < ksize) { + memset(dst + size, 0, rest); + } else if (usize > ksize) { + int ret = check_zeroed_user(src + size, rest); + if (ret <= 0) + return ret ?: -E2BIG; + } + /* Copy the interoperable parts of the struct. */ + if (copy_from_user(dst, src, size)) + return -EFAULT; + return 0; +} + /* * probe_kernel_read(): safely attempt to read from a location * @dst: pointer to the buffer that shall take the data diff --git a/lib/strnlen_user.c b/lib/strnlen_user.c index 28ff554a1be8..6c0005d5dd5c 100644 --- a/lib/strnlen_user.c +++ b/lib/strnlen_user.c @@ -3,16 +3,10 @@ #include <linux/export.h> #include <linux/uaccess.h> #include <linux/mm.h> +#include <linux/bitops.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 << (BITS_PER_LONG - 8 - 8*(n))) -#endif - /* * Do a strnlen, return length of string *with* final '\0'. * 'count' is the user-supplied count, while 'max' is the diff --git a/lib/test_user_copy.c b/lib/test_user_copy.c index 67bcd5dfd847..950ee88cd6ac 100644 --- a/lib/test_user_copy.c +++ b/lib/test_user_copy.c @@ -31,14 +31,133 @@ # define TEST_U64 #endif -#define test(condition, msg) \ -({ \ - int cond = (condition); \ - if (cond) \ - pr_warn("%s\n", msg); \ - cond; \ +#define test(condition, msg, ...) \ +({ \ + int cond = (condition); \ + if (cond) \ + pr_warn("[%d] " msg "\n", __LINE__, ##__VA_ARGS__); \ + cond; \ }) +static bool is_zeroed(void *from, size_t size) +{ + return memchr_inv(from, 0x0, size) == NULL; +} + +static int test_check_nonzero_user(char *kmem, char __user *umem, size_t size) +{ + int ret = 0; + size_t start, end, i; + size_t zero_start = size / 4; + size_t zero_end = size - zero_start; + + /* + * We conduct a series of check_nonzero_user() tests on a block of memory + * with the following byte-pattern (trying every possible [start,end] + * pair): + * + * [ 00 ff 00 ff ... 00 00 00 00 ... ff 00 ff 00 ] + * + * And we verify that check_nonzero_user() acts identically to memchr_inv(). + */ + + memset(kmem, 0x0, size); + for (i = 1; i < zero_start; i += 2) + kmem[i] = 0xff; + for (i = zero_end; i < size; i += 2) + kmem[i] = 0xff; + + ret |= test(copy_to_user(umem, kmem, size), + "legitimate copy_to_user failed"); + + for (start = 0; start <= size; start++) { + for (end = start; end <= size; end++) { + size_t len = end - start; + int retval = check_zeroed_user(umem + start, len); + int expected = is_zeroed(kmem + start, len); + + ret |= test(retval != expected, + "check_nonzero_user(=%d) != memchr_inv(=%d) mismatch (start=%zu, end=%zu)", + retval, expected, start, end); + } + } + + return ret; +} + +static int test_copy_struct_from_user(char *kmem, char __user *umem, + size_t size) +{ + int ret = 0; + char *umem_src = NULL, *expected = NULL; + size_t ksize, usize; + + umem_src = kmalloc(size, GFP_KERNEL); + if (ret |= test(umem_src == NULL, "kmalloc failed")) + goto out_free; + + expected = kmalloc(size, GFP_KERNEL); + if (ret |= test(expected == NULL, "kmalloc failed")) + goto out_free; + + /* Fill umem with a fixed byte pattern. */ + memset(umem_src, 0x3e, size); + ret |= test(copy_to_user(umem, umem_src, size), + "legitimate copy_to_user failed"); + + /* Check basic case -- (usize == ksize). */ + ksize = size; + usize = size; + + memcpy(expected, umem_src, ksize); + + memset(kmem, 0x0, size); + ret |= test(copy_struct_from_user(kmem, ksize, umem, usize), + "copy_struct_from_user(usize == ksize) failed"); + ret |= test(memcmp(kmem, expected, ksize), + "copy_struct_from_user(usize == ksize) gives unexpected copy"); + + /* Old userspace case -- (usize < ksize). */ + ksize = size; + usize = size / 2; + + memcpy(expected, umem_src, usize); + memset(expected + usize, 0x0, ksize - usize); + + memset(kmem, 0x0, size); + ret |= test(copy_struct_from_user(kmem, ksize, umem, usize), + "copy_struct_from_user(usize < ksize) failed"); + ret |= test(memcmp(kmem, expected, ksize), + "copy_struct_from_user(usize < ksize) gives unexpected copy"); + + /* New userspace (-E2BIG) case -- (usize > ksize). */ + ksize = size / 2; + usize = size; + + memset(kmem, 0x0, size); + ret |= test(copy_struct_from_user(kmem, ksize, umem, usize) != -E2BIG, + "copy_struct_from_user(usize > ksize) didn't give E2BIG"); + + /* New userspace (success) case -- (usize > ksize). */ + ksize = size / 2; + usize = size; + + memcpy(expected, umem_src, ksize); + ret |= test(clear_user(umem + ksize, usize - ksize), + "legitimate clear_user failed"); + + memset(kmem, 0x0, size); + ret |= test(copy_struct_from_user(kmem, ksize, umem, usize), + "copy_struct_from_user(usize > ksize) failed"); + ret |= test(memcmp(kmem, expected, ksize), + "copy_struct_from_user(usize > ksize) gives unexpected copy"); + +out_free: + kfree(expected); + kfree(umem_src); + return ret; +} + static int __init test_user_copy_init(void) { int ret = 0; @@ -106,6 +225,11 @@ static int __init test_user_copy_init(void) #endif #undef test_legit + /* Test usage of check_nonzero_user(). */ + ret |= test_check_nonzero_user(kmem, usermem, 2 * PAGE_SIZE); + /* Test usage of copy_struct_from_user(). */ + ret |= test_copy_struct_from_user(kmem, usermem, 2 * PAGE_SIZE); + /* * Invalid usage: none of these copies should succeed. */ diff --git a/lib/usercopy.c b/lib/usercopy.c index c2bfbcaeb3dc..cbb4d9ec00f2 100644 --- a/lib/usercopy.c +++ b/lib/usercopy.c @@ -1,5 +1,6 @@ // SPDX-License-Identifier: GPL-2.0 #include <linux/uaccess.h> +#include <linux/bitops.h> /* out-of-line parts */ @@ -31,3 +32,57 @@ unsigned long _copy_to_user(void __user *to, const void *from, unsigned long n) } EXPORT_SYMBOL(_copy_to_user); #endif + +/** + * check_zeroed_user: check if a userspace buffer only contains zero bytes + * @from: Source address, in userspace. + * @size: Size of buffer. + * + * This is effectively shorthand for "memchr_inv(from, 0, size) == NULL" for + * userspace addresses (and is more efficient because we don't care where the + * first non-zero byte is). + * + * Returns: + * * 0: There were non-zero bytes present in the buffer. + * * 1: The buffer was full of zero bytes. + * * -EFAULT: access to userspace failed. + */ +int check_zeroed_user(const void __user *from, size_t size) +{ + unsigned long val; + uintptr_t align = (uintptr_t) from % sizeof(unsigned long); + + if (unlikely(size == 0)) + return 1; + + from -= align; + size += align; + + if (!user_access_begin(from, size)) + return -EFAULT; + + unsafe_get_user(val, (unsigned long __user *) from, err_fault); + if (align) + val &= ~aligned_byte_mask(align); + + while (size > sizeof(unsigned long)) { + if (unlikely(val)) + goto done; + + from += sizeof(unsigned long); + size -= sizeof(unsigned long); + + unsafe_get_user(val, (unsigned long __user *) from, err_fault); + } + + if (size < sizeof(unsigned long)) + val &= aligned_byte_mask(size); + +done: + user_access_end(); + return (val == 0); +err_fault: + user_access_end(); + return -EFAULT; +} +EXPORT_SYMBOL(check_zeroed_user); |