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[patch] xfs: underflow bug in xfs_attrlist_by_handle()

To: Ben Myers <bpm@xxxxxxx>
Subject: [patch] xfs: underflow bug in xfs_attrlist_by_handle()
From: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Date: Thu, 31 Oct 2013 21:00:10 +0300
Cc: Alex Elder <elder@xxxxxxxxxx>, xfs@xxxxxxxxxxx, security@xxxxxxxxxx, Nico Golde <nico@xxxxxxxxx>, Fabian Yamaguchi <fabs@xxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20131025144452.GA28451@xxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
If we allocate less than sizeof(struct attrlist) then we end up
corrupting memory or doing a ZERO_PTR_SIZE dereference.

This can only be triggered with CAP_SYS_ADMIN.

Reported-by: Nico Golde <nico@xxxxxxxxx>
Reported-by: Fabian Yamaguchi <fabs@xxxxxxxxx>
Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>

diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
index 4d61340..33ad9a7 100644
--- a/fs/xfs/xfs_ioctl.c
+++ b/fs/xfs/xfs_ioctl.c
@@ -442,7 +442,8 @@ xfs_attrlist_by_handle(
                return -XFS_ERROR(EPERM);
        if (copy_from_user(&al_hreq, arg, 
sizeof(xfs_fsop_attrlist_handlereq_t)))
                return -XFS_ERROR(EFAULT);
-       if (al_hreq.buflen > XATTR_LIST_MAX)
+       if (al_hreq.buflen < sizeof(struct attrlist) ||
+           al_hreq.buflen > XATTR_LIST_MAX)
                return -XFS_ERROR(EINVAL);
 
        /*
diff --git a/fs/xfs/xfs_ioctl32.c b/fs/xfs/xfs_ioctl32.c
index e8fb123..a7992f8 100644
--- a/fs/xfs/xfs_ioctl32.c
+++ b/fs/xfs/xfs_ioctl32.c
@@ -356,7 +356,8 @@ xfs_compat_attrlist_by_handle(
        if (copy_from_user(&al_hreq, arg,
                           sizeof(compat_xfs_fsop_attrlist_handlereq_t)))
                return -XFS_ERROR(EFAULT);
-       if (al_hreq.buflen > XATTR_LIST_MAX)
+       if (al_hreq.buflen < sizeof(struct attrlist) ||
+           al_hreq.buflen > XATTR_LIST_MAX)
                return -XFS_ERROR(EINVAL);
 
        /*

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