lib: Reduce user_access_begin() boundaries in strncpy_from_user() and strnlen_user()
The range passed to user_access_begin() by strncpy_from_user() and
strnlen_user() starts at 'src' and goes up to the limit of userspace
although reads will be limited by the 'count' param.
On 32 bits powerpc (book3s/32) access has to be granted for each
256Mbytes segment and the cost increases with the number of segments to
unlock.
Limit the range with 'count' param.
Fixes: 594cc251fd
("make 'user_access_begin()' do 'access_ok()'")
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@ -30,13 +30,6 @@ static inline long do_strncpy_from_user(char *dst, const char __user *src,
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const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
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unsigned long res = 0;
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/*
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* Truncate 'max' to the user-specified limit, so that
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* we only have one limit we need to check in the loop
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*/
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if (max > count)
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max = count;
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if (IS_UNALIGNED(src, dst))
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goto byte_at_a_time;
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@ -114,6 +107,13 @@ long strncpy_from_user(char *dst, const char __user *src, long count)
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unsigned long max = max_addr - src_addr;
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long retval;
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/*
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* Truncate 'max' to the user-specified limit, so that
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* we only have one limit we need to check in the loop
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*/
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if (max > count)
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max = count;
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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(src, max)) {
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@ -26,13 +26,6 @@ static inline long do_strnlen_user(const char __user *src, unsigned long count,
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unsigned long align, res = 0;
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unsigned long c;
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/*
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* Truncate 'max' to the user-specified limit, so that
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* we only have one limit we need to check in the loop
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*/
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if (max > count)
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max = count;
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/*
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* Do everything aligned. But that means that we
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* need to also expand the maximum..
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@ -109,6 +102,13 @@ long strnlen_user(const char __user *str, long count)
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unsigned long max = max_addr - src_addr;
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long retval;
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/*
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* Truncate 'max' to the user-specified limit, so that
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* we only have one limit we need to check in the loop
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*/
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if (max > count)
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max = count;
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if (user_access_begin(str, max)) {
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retval = do_strnlen_user(str, count, max);
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user_access_end();
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