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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-11 08:27:49 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-11 08:27:49 +0000 |
commit | ace9429bb58fd418f0c81d4c2835699bddf6bde6 (patch) | |
tree | b2d64bc10158fdd5497876388cd68142ca374ed3 /lib/strncpy_from_user.c | |
parent | Initial commit. (diff) | |
download | linux-ace9429bb58fd418f0c81d4c2835699bddf6bde6.tar.xz linux-ace9429bb58fd418f0c81d4c2835699bddf6bde6.zip |
Adding upstream version 6.6.15.upstream/6.6.15
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to '')
-rw-r--r-- | lib/strncpy_from_user.c | 146 |
1 files changed, 146 insertions, 0 deletions
diff --git a/lib/strncpy_from_user.c b/lib/strncpy_from_user.c new file mode 100644 index 0000000000..6432b8c3e4 --- /dev/null +++ b/lib/strncpy_from_user.c @@ -0,0 +1,146 @@ +// SPDX-License-Identifier: GPL-2.0 +#include <linux/compiler.h> +#include <linux/export.h> +#include <linux/fault-inject-usercopy.h> +#include <linux/kasan-checks.h> +#include <linux/thread_info.h> +#include <linux/uaccess.h> +#include <linux/kernel.h> +#include <linux/errno.h> +#include <linux/mm.h> + +#include <asm/byteorder.h> +#include <asm/word-at-a-time.h> + +#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS +#define IS_UNALIGNED(src, dst) 0 +#else +#define IS_UNALIGNED(src, dst) \ + (((long) dst | (long) src) & (sizeof(long) - 1)) +#endif + +/* + * Do a strncpy, return length of string without final '\0'. + * 'count' is the user-supplied count (return 'count' if we + * hit it), 'max' is the address space maximum (and we return + * -EFAULT if we hit it). + */ +static __always_inline long do_strncpy_from_user(char *dst, const char __user *src, + unsigned long count, unsigned long max) +{ + const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS; + unsigned long res = 0; + + if (IS_UNALIGNED(src, dst)) + goto byte_at_a_time; + + while (max >= sizeof(unsigned long)) { + unsigned long c, data, mask; + + /* Fall back to byte-at-a-time if we get a page fault */ + unsafe_get_user(c, (unsigned long __user *)(src+res), byte_at_a_time); + + /* + * Note that we mask out the bytes following the NUL. This is + * important to do because string oblivious code may read past + * the NUL. For those routines, we don't want to give them + * potentially random bytes after the NUL in `src`. + * + * One example of such code is BPF map keys. BPF treats map keys + * as an opaque set of bytes. Without the post-NUL mask, any BPF + * maps keyed by strings returned from strncpy_from_user() may + * have multiple entries for semantically identical strings. + */ + if (has_zero(c, &data, &constants)) { + data = prep_zero_mask(c, data, &constants); + data = create_zero_mask(data); + mask = zero_bytemask(data); + *(unsigned long *)(dst+res) = c & mask; + return res + find_zero(data); + } + + *(unsigned long *)(dst+res) = c; + + res += sizeof(unsigned long); + max -= sizeof(unsigned long); + } + +byte_at_a_time: + while (max) { + char c; + + unsafe_get_user(c,src+res, efault); + dst[res] = c; + if (!c) + return res; + res++; + max--; + } + + /* + * Uhhuh. We hit 'max'. But was that the user-specified maximum + * too? If so, that's ok - we got as much as the user asked for. + */ + if (res >= count) + return res; + + /* + * Nope: we hit the address space limit, and we still had more + * characters the caller would have wanted. That's an EFAULT. + */ +efault: + return -EFAULT; +} + +/** + * strncpy_from_user: - Copy a NUL terminated string from userspace. + * @dst: Destination address, in kernel space. This buffer must be at + * least @count bytes long. + * @src: Source address, in user space. + * @count: Maximum number of bytes to copy, including the trailing NUL. + * + * Copies a NUL-terminated string from userspace to kernel space. + * + * On success, returns the length of the string (not including the trailing + * NUL). + * + * If access to userspace fails, returns -EFAULT (some data may have been + * copied). + * + * If @count is smaller than the length of the string, copies @count bytes + * and returns @count. + */ +long strncpy_from_user(char *dst, const char __user *src, long count) +{ + unsigned long max_addr, src_addr; + + might_fault(); + if (should_fail_usercopy()) + return -EFAULT; + if (unlikely(count <= 0)) + return 0; + + max_addr = TASK_SIZE_MAX; + src_addr = (unsigned long)untagged_addr(src); + if (likely(src_addr < max_addr)) { + unsigned long max = max_addr - src_addr; + long retval; + + /* + * 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; + + kasan_check_write(dst, count); + check_object_size(dst, count, false); + if (user_read_access_begin(src, max)) { + retval = do_strncpy_from_user(dst, src, count, max); + user_read_access_end(); + return retval; + } + } + return -EFAULT; +} +EXPORT_SYMBOL(strncpy_from_user); |