2022-04-12 19:42:06

by Harshit Mogalapalli

Subject: [PATCH] cifs: potential buffer overflow in handling symlinks

Smatch printed a warning:
arch/x86/crypto/poly1305_glue.c:198 poly1305_update_arch() error:
__memcpy() 'dctx->buf' too small (16 vs u32max)

It's caused because Smatch marks 'link_len' as untrusted since it comes
from sscanf(). Add a check to ensure that 'link_len' is not larger than
the size of the 'link_str' buffer.

Fixes: c69c1b6eaea1 ("cifs: implement CIFSParseMFSymlink()")
Signed-off-by: Harshit Mogalapalli <[email protected]>
---
fs/cifs/link.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/fs/cifs/link.c b/fs/cifs/link.c
index 852e54e..ebfedae 100644
--- a/fs/cifs/link.c
+++ b/fs/cifs/link.c
@@ -85,6 +85,9 @@
if (rc != 1)
return -EINVAL;

+ if (link_len > buf_len - CIFS_MF_SYMLINK_LINK_OFFSET)
+ return -EINVAL;
+
rc = symlink_hash(link_len, link_str, md5_hash);
if (rc) {
cifs_dbg(FYI, "%s: MD5 hash failure: %d\n", __func__, rc);
--
1.8.3.1

2022-04-13 00:12:44

by Steve French

Subject: Re: [PATCH] cifs: potential buffer overflow in handling symlinks

Wouldn't it be easier and clearer to do the compare vs the maximum len ie

if (link_len > CIFS_MF_SYMLINK_LINK_MAXLEN)

instead of

if (link_len > buf_len - CIFS_MF_SYMLINK_LINK_OFFSET)

since buf_len is CIFS_MF_SYMLINK_FILE_SIZE and looking at link.c line
26 and 27 this means we can use CIFS_MF_SYMLINK_LINK_OFFSET for the
comparison:

#define CIFS_MF_SYMLINK_LINK_MAXLEN (1024)
#define CIFS_MF_SYMLINK_FILE_SIZE \
(CIFS_MF_SYMLINK_LINK_OFFSET + CIFS_MF_SYMLINK_LINK_MAXLEN)

On Tue, Apr 12, 2022 at 1:01 AM Harshit Mogalapalli
<[email protected]> wrote:
>
> Smatch printed a warning:
> arch/x86/crypto/poly1305_glue.c:198 poly1305_update_arch() error:
> __memcpy() 'dctx->buf' too small (16 vs u32max)
>
> It's caused because Smatch marks 'link_len' as untrusted since it comes
> from sscanf(). Add a check to ensure that 'link_len' is not larger than
> the size of the 'link_str' buffer.
>
> Fixes: c69c1b6eaea1 ("cifs: implement CIFSParseMFSymlink()")
> Signed-off-by: Harshit Mogalapalli <[email protected]>
> ---
> fs/cifs/link.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/fs/cifs/link.c b/fs/cifs/link.c
> index 852e54e..ebfedae 100644
> --- a/fs/cifs/link.c
> +++ b/fs/cifs/link.c
> @@ -85,6 +85,9 @@
> if (rc != 1)
> return -EINVAL;
>
> + if (link_len > buf_len - CIFS_MF_SYMLINK_LINK_OFFSET)
> + return -EINVAL;
> +
> rc = symlink_hash(link_len, link_str, md5_hash);
> if (rc) {
> cifs_dbg(FYI, "%s: MD5 hash failure: %d\n", __func__, rc);
> --
> 1.8.3.1
>


--
Thanks,

Steve

2022-04-13 14:43:28

by Harshit Mogalapalli

Subject: Re: [PATCH] cifs: potential buffer overflow in handling symlinks

Hi Steve,
On 13/04/22 4:02 am, Steve French wrote:
> Wouldn't it be easier and clearer to do the compare vs the maximum len ie
>
> if (link_len > CIFS_MF_SYMLINK_LINK_MAXLEN)
>
Yes, thats cleaner. Will send a v2 patch.

Thanks,
Harshit
> instead of
>
> if (link_len > buf_len - CIFS_MF_SYMLINK_LINK_OFFSET)
>
> since buf_len is CIFS_MF_SYMLINK_FILE_SIZE and looking at link.c line
> 26 and 27 this means we can use CIFS_MF_SYMLINK_LINK_OFFSET for the
> comparison:
>
> #define CIFS_MF_SYMLINK_LINK_MAXLEN (1024)
> #define CIFS_MF_SYMLINK_FILE_SIZE \
> (CIFS_MF_SYMLINK_LINK_OFFSET + CIFS_MF_SYMLINK_LINK_MAXLEN)
>
> On Tue, Apr 12, 2022 at 1:01 AM Harshit Mogalapalli
> <[email protected]> wrote:
>>
>> Smatch printed a warning:
>> arch/x86/crypto/poly1305_glue.c:198 poly1305_update_arch() error:
>> __memcpy() 'dctx->buf' too small (16 vs u32max)
>>
>> It's caused because Smatch marks 'link_len' as untrusted since it comes
>> from sscanf(). Add a check to ensure that 'link_len' is not larger than
>> the size of the 'link_str' buffer.
>>
>> Fixes: c69c1b6eaea1 ("cifs: implement CIFSParseMFSymlink()")
>> Signed-off-by: Harshit Mogalapalli <[email protected]>
>> ---
>> fs/cifs/link.c | 3 +++
>> 1 file changed, 3 insertions(+)
>>
>> diff --git a/fs/cifs/link.c b/fs/cifs/link.c
>> index 852e54e..ebfedae 100644
>> --- a/fs/cifs/link.c
>> +++ b/fs/cifs/link.c
>> @@ -85,6 +85,9 @@
>> if (rc != 1)
>> return -EINVAL;
>>
>> + if (link_len > buf_len - CIFS_MF_SYMLINK_LINK_OFFSET)
>> + return -EINVAL;
>> +
>> rc = symlink_hash(link_len, link_str, md5_hash);
>> if (rc) {
>> cifs_dbg(FYI, "%s: MD5 hash failure: %d\n", __func__, rc);
>> --
>> 1.8.3.1
>>
>
>