[PATCH] smb: client: fix ALIGN() overflow in symlink_data() error context loop

[PATCH] smb: client: fix ALIGN() overflow in symlink_data() error context loop

[Frank Sorenson]

The check added by commit 7d9a7f1f96cd compared the post-ALIGN length
against the remaining buffer, but ALIGN() itself can overflow: for
ErrorDataLength near UINT32_MAX (e.g. 0xFFFFFFF9), ALIGN(x, 8) wraps
to 0, so the subsequent bounds check passes, and the loop advances by
zero bytes leaving 'p' pointing into stale data.

Fix by checking the raw ErrorDataLength against the remaining space
before applying ALIGN(), then checking again after.  Since raw_len is
bounded by the buffer, raw_len + 7 cannot overflow, so the second check
is an exact post-alignment bounds guard.

Fixes: 76894f3e2f71 ("cifs: improve symlink handling for smb2+")
Cc: stable@vger.kernel.org
Signed-off-by: Frank Sorenson <sorenson@redhat.com>
---
 fs/smb/client/smb2file.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/smb/client/smb2file.c b/fs/smb/client/smb2file.c
index f35b6488d810..fb2fccbe8667 100644
--- a/fs/smb/client/smb2file.c
+++ b/fs/smb/client/smb2file.c
@@ -61,7 +61,10 @@ static struct smb2_symlink_err_rsp *symlink_data(const struct kvec *iov)
 			cifs_dbg(FYI, "%s: skipping unhandled error context: 0x%x\n",
 				 __func__, le32_to_cpu(p->ErrorId));
 
-			len = ALIGN(le32_to_cpu(p->ErrorDataLength), 8);
+			len = le32_to_cpu(p->ErrorDataLength);
+			if (len > end - ((u8 *)p + sizeof(*p)))
+				return ERR_PTR(-EINVAL);
+			len = ALIGN(len, 8);
 			if (len > end - ((u8 *)p + sizeof(*p)))
 				return ERR_PTR(-EINVAL);
 
-- 
2.55.0

Re: [PATCH] smb: client: fix ALIGN() overflow in symlink_data() error context loop

[Paulo Alcantara]

Frank Sorenson <sorenson@redhat.com> writes:

> The check added by commit 7d9a7f1f96cd compared the post-ALIGN length
> against the remaining buffer, but ALIGN() itself can overflow: for
> ErrorDataLength near UINT32_MAX (e.g. 0xFFFFFFF9), ALIGN(x, 8) wraps
> to 0, so the subsequent bounds check passes, and the loop advances by
> zero bytes leaving 'p' pointing into stale data.
>
> Fix by checking the raw ErrorDataLength against the remaining space
> before applying ALIGN(), then checking again after.  Since raw_len is
> bounded by the buffer, raw_len + 7 cannot overflow, so the second check
> is an exact post-alignment bounds guard.
>
> Fixes: 76894f3e2f71 ("cifs: improve symlink handling for smb2+")
> Cc: stable@vger.kernel.org
> Signed-off-by: Frank Sorenson <sorenson@redhat.com>

Acked-by: Paulo Alcantara (Red Hat) <pc@manguebit.org>

Re: [PATCH] smb: client: fix ALIGN() overflow in symlink_data() error context loop

[Namjae Jeon]

On Tue, Aug 18, 2026 at 2:17 AM Frank Sorenson <sorenson@redhat.com> wrote:
>
> The check added by commit 7d9a7f1f96cd compared the post-ALIGN length
> against the remaining buffer, but ALIGN() itself can overflow: for
> ErrorDataLength near UINT32_MAX (e.g. 0xFFFFFFF9), ALIGN(x, 8) wraps
> to 0, so the subsequent bounds check passes, and the loop advances by
> zero bytes leaving 'p' pointing into stale data.
>
> Fix by checking the raw ErrorDataLength against the remaining space
> before applying ALIGN(), then checking again after.  Since raw_len is
> bounded by the buffer, raw_len + 7 cannot overflow, so the second check
> is an exact post-alignment bounds guard.
>
> Fixes: 76894f3e2f71 ("cifs: improve symlink handling for smb2+")
> Cc: stable@vger.kernel.org
> Signed-off-by: Frank Sorenson <sorenson@redhat.com>
Will appy it to #for-next with Paulo's acked-by tag.
Thanks!