Re: [PATCH] MIPS: Fix strnlen_user access check

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On 04/11/2021 07:04 PM, Jinyang He wrote:
Commit 04324f44cb69 ("MIPS: Remove get_fs/set_fs") brought a problem for
strnlen_user(). Jump out when checking access_ok() with condition that
(s + strlen(s)) < __UA_LIMIT <= (s + n). The old __strnlen_user_asm()
just checked (ua_limit & s) without checking (ua_limit & (s + n)).
Therefore, find strlen form s to __UA_LIMIT - 1 in that condition.

Signed-off-by: Jinyang He <hejinyang@xxxxxxxxxxx>
---
  arch/mips/include/asm/uaccess.h | 11 +++++++++--
  1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/arch/mips/include/asm/uaccess.h b/arch/mips/include/asm/uaccess.h
index 91bc7fb..85ba0c8 100644
--- a/arch/mips/include/asm/uaccess.h
+++ b/arch/mips/include/asm/uaccess.h
@@ -630,8 +630,15 @@ static inline long strnlen_user(const char __user *s, long n)
  {
  	long res;
- if (!access_ok(s, n))
-		return -0;
+	if (unlikely(n <= 0))
+		return 0;
+
+	if (!access_ok(s, n)) {
+		if (!access_ok(s, 0))
+			return 0;
+
+		n = __UA_LIMIT - (unsigned long)s - 1;
Sorry for here and it should be ~__UA_LIMIT...
earlier discussed:
https://patchwork.kernel.org/project/linux-mips/patch/1618139092-4018-1-git-send-email-hejinyang@xxxxxxxxxxx/#24107107

Hope other comment. :-)

Jinyang

+	}
might_fault();
  	__asm__ __volatile__(




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