[PATCH] fat: Read buffer overflow

[PATCH] fat: Read buffer overflow

[Roel Kluin]

If len is less or equal to 0, this results in a read of s[-1].

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
---
diff --git a/fs/fat/namei_vfat.c b/fs/fat/namei_vfat.c
index 6f27853..114ff6d 100644
--- a/fs/fat/namei_vfat.c
+++ b/fs/fat/namei_vfat.c
@@ -202,6 +202,9 @@ static inline int vfat_is_used_badchars(const wchar_t *s, int len)
 {
 	int i;
 
+	if (len <= 0)
+		return -EINVAL;
+
 	for (i = 0; i < len; i++)
 		if (vfat_bad_char(s[i]))
 			return -EINVAL;

Re: [PATCH] fat: Read buffer overflow

[OGAWA Hirofumi]

Roel Kluin <roel.kluin@gmail.com> writes:

> If len is less or equal to 0, this results in a read of s[-1].
>
> Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
> ---
> diff --git a/fs/fat/namei_vfat.c b/fs/fat/namei_vfat.c
> index 6f27853..114ff6d 100644
> --- a/fs/fat/namei_vfat.c
> +++ b/fs/fat/namei_vfat.c
> @@ -202,6 +202,9 @@ static inline int vfat_is_used_badchars(const wchar_t *s, int len)
>  {
>  	int i;
>  
> +	if (len <= 0)
> +		return -EINVAL;
> +
>  	for (i = 0; i < len; i++)
>  		if (vfat_bad_char(s[i]))
>  			return -EINVAL;

Um..., what case is this possible? vfat_add_entry() checks (len == 0).
And if xlate_to_uni() couldn't convert name, it should return the error.

Thanks.
-- 
OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>

Re: [PATCH] fat: Read buffer overflow

[Pekka Enberg]

Hi Hirofumi-san,

Roel Kluin <roel.kluin@gmail.com> writes:
>> If len is less or equal to 0, this results in a read of s[-1].
>>
>> Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
>> ---
>> diff --git a/fs/fat/namei_vfat.c b/fs/fat/namei_vfat.c
>> index 6f27853..114ff6d 100644
>> --- a/fs/fat/namei_vfat.c
>> +++ b/fs/fat/namei_vfat.c
>> @@ -202,6 +202,9 @@ static inline int vfat_is_used_badchars(const wchar_t *s, int len)
>>  {
>>       int i;
>>
>> +     if (len <= 0)
>> +             return -EINVAL;
>> +
>>       for (i = 0; i < len; i++)
>>               if (vfat_bad_char(s[i]))
>>                       return -EINVAL;

On Sat, Aug 8, 2009 at 2:06 AM, OGAWA
Hirofumi<hirofumi@mail.parknet.co.jp> wrote:
> Um..., what case is this possible? vfat_add_entry() checks (len == 0).
> And if xlate_to_uni() couldn't convert name, it should return the error.

Yes, but we pass "ulen" to vfat_is_used_badchars(). The value of
"ulen" is a returned in the "longlen" argument of xlate_to_uni() which
in turn is calculated as follows for the UTF-8 case:

  int name_len = strlen(name);
  *outlen = utf8s_to_utf16s(name, PATH_MAX, (wchar_t *) outname);
  *outlen -= (name_len - len);
  *longlen = *outlen;

Maybe "*outlen" can never be negative because of some invariants that
I don't see but it's so non-obvious to me that I'd like to see the
explicit check in vfat_is_used_badchars().

                        Pekka

Re: [PATCH] fat: Read buffer overflow

[OGAWA Hirofumi]

Pekka Enberg <penberg@cs.helsinki.fi> writes:

> Yes, but we pass "ulen" to vfat_is_used_badchars(). The value of
> "ulen" is a returned in the "longlen" argument of xlate_to_uni() which
> in turn is calculated as follows for the UTF-8 case:
>
>   int name_len = strlen(name);
>   *outlen = utf8s_to_utf16s(name, PATH_MAX, (wchar_t *) outname);
>   *outlen -= (name_len - len);
>   *longlen = *outlen;
>
> Maybe "*outlen" can never be negative because of some invariants that
> I don't see but it's so non-obvious to me that I'd like to see the
> explicit check in vfat_is_used_badchars().

Ah, good point. Sorry, I was looking my tree. I'm going to submit the
attached patch on next merge window.

Is this enough for it?

Thanks.
-- 
OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>


With utf8 option, vfat allowed the duplicated filenames.

Normal nls returns -EINVAL for invalid char. But utf8s_to_utf16s()
skipped the invalid char historically.

So, this changes the utf8s_to_utf16s() directly to return -EINVAL for
invalid char, because vfat is only user of it.


mkdir /mnt/fatfs
FILENAME=`echo -ne "invalidutf8char_\\0341_endofchar"`
echo "Using filename: $FILENAME"
dd if=/dev/zero of=fatfs bs=512 count=128
mkdosfs -F 32 fatfs
mount -o loop,utf8 fatfs /mnt/fatfs
touch "/mnt/fatfs/$FILENAME"
umount /mnt/fatfs
mount -o loop,utf8 fatfs /mnt/fatfs
touch "/mnt/fatfs/$FILENAME"
ls -l /mnt/fatfs
umount /mnt/fatfs

----  And the output is:

Using filename: invalidutf8char_\0341_endofchar
128+0 records in
128+0 records out
65536 bytes (66 kB) copied, 0.000388118 s, 169 MB/s
mkdosfs 2.11 (12 Mar 2005)
total 0
-rwxr-xr-x 1 root root 0 Jun 28 19:46 invalidutf8char__endofchar
-rwxr-xr-x 1 root root 0 Jun 28 19:46 invalidutf8char__endofchar

Tested-by: Marton Balint <cus@fazekas.hu>
Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
---

 fs/fat/namei_vfat.c |   15 ++++-----------
 fs/nls/nls_base.c   |    8 ++++----
 2 files changed, 8 insertions(+), 15 deletions(-)

diff -puN fs/fat/namei_vfat.c~vfat-utf8-invalid-char fs/fat/namei_vfat.c
--- linux-2.6/fs/fat/namei_vfat.c~vfat-utf8-invalid-char	2009-08-01 15:25:36.000000000 +0900
+++ linux-2.6-hirofumi/fs/fat/namei_vfat.c	2009-08-01 21:26:42.000000000 +0900
@@ -499,17 +499,10 @@ xlate_to_uni(const unsigned char *name, 
 	int charlen;
 
 	if (utf8) {
-		int name_len = strlen(name);
-
-		*outlen = utf8s_to_utf16s(name, PATH_MAX, (wchar_t *) outname);
-
-		/*
-		 * We stripped '.'s before and set len appropriately,
-		 * but utf8s_to_utf16s doesn't care about len
-		 */
-		*outlen -= (name_len - len);
-
-		if (*outlen > 255)
+		*outlen = utf8s_to_utf16s(name, len, (wchar_t *)outname);
+		if (*outlen < 0)
+			return *outlen;
+		else if (*outlen > 255)
 			return -ENAMETOOLONG;
 
 		op = &outname[*outlen * sizeof(wchar_t)];
diff -puN fs/nls/nls_base.c~vfat-utf8-invalid-char fs/nls/nls_base.c
--- linux-2.6/fs/nls/nls_base.c~vfat-utf8-invalid-char	2009-08-01 15:25:36.000000000 +0900
+++ linux-2.6-hirofumi/fs/nls/nls_base.c	2009-08-01 15:25:36.000000000 +0900
@@ -124,10 +124,10 @@ int utf8s_to_utf16s(const u8 *s, int len
 	while (*s && len > 0) {
 		if (*s & 0x80) {
 			size = utf8_to_utf32(s, len, &u);
-			if (size < 0) {
-				/* Ignore character and move on */
-				size = 1;
-			} else if (u >= PLANE_SIZE) {
+			if (size < 0)
+				return -EINVAL;
+
+			if (u >= PLANE_SIZE) {
 				u -= PLANE_SIZE;
 				*op++ = (wchar_t) (SURROGATE_PAIR |
 						((u >> 10) & SURROGATE_BITS));
_

Re: [PATCH] fat: Read buffer overflow

[Pekka Enberg]

On Sat, 2009-08-08 at 19:10 +0900, OGAWA Hirofumi wrote:
> Pekka Enberg <penberg@cs.helsinki.fi> writes:
> 
> > Yes, but we pass "ulen" to vfat_is_used_badchars(). The value of
> > "ulen" is a returned in the "longlen" argument of xlate_to_uni() which
> > in turn is calculated as follows for the UTF-8 case:
> >
> >   int name_len = strlen(name);
> >   *outlen = utf8s_to_utf16s(name, PATH_MAX, (wchar_t *) outname);
> >   *outlen -= (name_len - len);
> >   *longlen = *outlen;
> >
> > Maybe "*outlen" can never be negative because of some invariants that
> > I don't see but it's so non-obvious to me that I'd like to see the
> > explicit check in vfat_is_used_badchars().
> 
> Ah, good point. Sorry, I was looking my tree. I'm going to submit the
> attached patch on next merge window.
> 
> Is this enough for it?

Fine by me!

			Pekka

Re: [PATCH] fat: Read buffer overflow

[OGAWA Hirofumi]

OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> writes:

> Pekka Enberg <penberg@cs.helsinki.fi> writes:
>
>> Yes, but we pass "ulen" to vfat_is_used_badchars(). The value of
>> "ulen" is a returned in the "longlen" argument of xlate_to_uni() which
>> in turn is calculated as follows for the UTF-8 case:
>>
>>   int name_len = strlen(name);
>>   *outlen = utf8s_to_utf16s(name, PATH_MAX, (wchar_t *) outname);
>>   *outlen -= (name_len - len);
>>   *longlen = *outlen;
>>
>> Maybe "*outlen" can never be negative because of some invariants that
>> I don't see but it's so non-obvious to me that I'd like to see the
>> explicit check in vfat_is_used_badchars().
>
> Ah, good point. Sorry, I was looking my tree. I'm going to submit the
> attached patch on next merge window.
>
> Is this enough for it?

BTW, if we want the sanity check of "longlen", I'd like to put it in the
end of xlate_to_uni(), not vfat_is_used_badchars(). Because I think it's
job of xlate_to_uni().

Thanks.
-- 
OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>

Re: [PATCH] fat: Read buffer overflow

[Alexander Koeppe]

Roel Kluin schrieb:
> If len is less or equal to 0, this results in a read of s[-1].
> 
> Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
> ---
> diff --git a/fs/fat/namei_vfat.c b/fs/fat/namei_vfat.c
> index 6f27853..114ff6d 100644
> --- a/fs/fat/namei_vfat.c
> +++ b/fs/fat/namei_vfat.c
> @@ -202,6 +202,9 @@ static inline int vfat_is_used_badchars(const wchar_t *s, int len)
>  {
>  	int i;
>  
> +	if (len <= 0)
> +		return -EINVAL;
> +
>  	for (i = 0; i < len; i++)
>  		if (vfat_bad_char(s[i]))
>  			return -EINVAL;
> --
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This seem to be a bit redundant code.
If len is 0 or less, the loop won't iterate even one time and hence
not read outside the buffer.
The only advantage is, that re function signals the invalid argument.

-- A.Koeppe