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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>
This commit is contained in:
Christophe Leroy 2020-01-23 08:34:18 +00:00 committed by Linus Torvalds
parent 838a860a39
commit ab10ae1c3b
2 changed files with 14 additions and 14 deletions
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14
lib/strncpy_from_user.c
View File

@ -30,13 +30,6 @@ static inline long do_strncpy_from_user(char *dst, const char __user *src,
const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS; const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
unsigned long res = 0; unsigned long res = 0;
/*
* 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;
if (IS_UNALIGNED(src, dst)) if (IS_UNALIGNED(src, dst))
goto byte_at_a_time; goto byte_at_a_time;
@ -114,6 +107,13 @@ long strncpy_from_user(char *dst, const char __user *src, long count)
unsigned long max = max_addr - src_addr; unsigned long max = max_addr - src_addr;
long retval; 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); kasan_check_write(dst, count);
check_object_size(dst, count, false); check_object_size(dst, count, false);
if (user_access_begin(src, max)) { if (user_access_begin(src, max)) {

14
lib/strnlen_user.c
View File

@ -26,13 +26,6 @@ static inline long do_strnlen_user(const char __user *src, unsigned long count,
unsigned long align, res = 0; unsigned long align, res = 0;
unsigned long c; 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 * Do everything aligned. But that means that we
* need to also expand the maximum.. * need to also expand the maximum..
@ -109,6 +102,13 @@ long strnlen_user(const char __user *str, long count)
unsigned long max = max_addr - src_addr; unsigned long max = max_addr - src_addr;
long retval; 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;
if (user_access_begin(str, max)) { if (user_access_begin(str, max)) {
retval = do_strnlen_user(str, count, max); retval = do_strnlen_user(str, count, max);
user_access_end(); user_access_end();