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2023-12-08 01573e231f18eb2d99162747186f59511f56b64d

 kernel/lib/strncpy_from_user.c
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@@ -1,6 +1,7 @@
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 // SPDX-License-Identifier: GPL-2.0
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 #include <linux/compiler.h>
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 #include <linux/export.h>
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+#include <linux/fault-inject-usercopy.h>
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 #include <linux/kasan-checks.h>
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 #include <linux/thread_info.h>
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 #include <linux/uaccess.h>
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@@ -34,17 +35,32 @@
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 		goto byte_at_a_time;
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 	while (max >= sizeof(unsigned long)) {
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-		unsigned long c, data;
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+		unsigned long c, data, mask;
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 		/* Fall back to byte-at-a-time if we get a page fault */
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 		unsafe_get_user(c, (unsigned long __user *)(src+res), byte_at_a_time);
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-		*(unsigned long *)(dst+res) = c;
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+		/*
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+		 * Note that we mask out the bytes following the NUL. This is
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+		 * important to do because string oblivious code may read past
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+		 * the NUL. For those routines, we don't want to give them
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+		 * potentially random bytes after the NUL in `src`.
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+		 *
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+		 * One example of such code is BPF map keys. BPF treats map keys
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+		 * as an opaque set of bytes. Without the post-NUL mask, any BPF
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+		 * maps keyed by strings returned from strncpy_from_user() may
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+		 * have multiple entries for semantically identical strings.
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+		 */
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 		if (has_zero(c, &data, &constants)) {
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 			data = prep_zero_mask(c, data, &constants);
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 			data = create_zero_mask(data);
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+			mask = zero_bytemask(data);
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+			*(unsigned long *)(dst+res) = c & mask;
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 			return res + find_zero(data);
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 		}
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+
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+		*(unsigned long *)(dst+res) = c;
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+
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 		res += sizeof(unsigned long);
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 		max -= sizeof(unsigned long);
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 	}
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@@ -98,6 +114,9 @@
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 {
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 	unsigned long max_addr, src_addr;
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+	might_fault();
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+	if (should_fail_usercopy())
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+		return -EFAULT;
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 	if (unlikely(count <= 0))
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 		return 0;
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..
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@@ -116,9 +135,9 @@
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 		kasan_check_write(dst, count);
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 		check_object_size(dst, count, false);
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-		if (user_access_begin(VERIFY_READ, src, max)) {
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+		if (user_read_access_begin(src, max)) {
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 			retval = do_strncpy_from_user(dst, src, count, max);
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-			user_access_end();
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+			user_read_access_end();
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 			return retval;
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 		}
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 	}