[PATCH] afs: xattr: use scnprintf

[PATCH] afs: xattr: use scnprintf

[Mark Salyzyn]

sprintf and snprintf are fragile in future maintenance, switch to
using scnprintf to ensure no accidental Use After Free conditions
are introduced.

Signed-off-by: Mark Salyzyn <salyzyn@android.com>
Cc: linux-kernel@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org
Cc: David Howells <dhowells@redhat.com>
Cc: linux-afs@lists.infradead.org
Cc: Jan Kara <jack@suse.cz>
---
 fs/afs/xattr.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/fs/afs/xattr.c b/fs/afs/xattr.c
index 5552d034090a..7af41fd5f3ee 100644
--- a/fs/afs/xattr.c
+++ b/fs/afs/xattr.c
@@ -228,11 +228,11 @@ static int afs_xattr_get_yfs(const struct xattr_handler *handler,
 		break;
 	case 1:
 		data = buf;
-		dsize = snprintf(buf, sizeof(buf), "%u", yacl->inherit_flag);
+		dsize = scnprintf(buf, sizeof(buf), "%u", yacl->inherit_flag);
 		break;
 	case 2:
 		data = buf;
-		dsize = snprintf(buf, sizeof(buf), "%u", yacl->num_cleaned);
+		dsize = scnprintf(buf, sizeof(buf), "%u", yacl->num_cleaned);
 		break;
 	case 3:
 		data = yacl->vol_acl->data;
@@ -370,13 +370,15 @@ static int afs_xattr_get_fid(const struct xattr_handler *handler,
 	/* The volume ID is 64-bit, the vnode ID is 96-bit and the
 	 * uniquifier is 32-bit.
 	 */
-	len = sprintf(text, "%llx:", vnode->fid.vid);
+	len = scnprintf(text, sizeof(text), "%llx:", vnode->fid.vid);
 	if (vnode->fid.vnode_hi)
-		len += sprintf(text + len, "%x%016llx",
-			       vnode->fid.vnode_hi, vnode->fid.vnode);
+		len += scnprintf(text + len, sizeof(text) - len, "%x%016llx",
+				vnode->fid.vnode_hi, vnode->fid.vnode);
 	else
-		len += sprintf(text + len, "%llx", vnode->fid.vnode);
-	len += sprintf(text + len, ":%x", vnode->fid.unique);
+		len += scnprintf(text + len, sizeof(text) - len, "%llx",
+				 vnode->fid.vnode);
+	len += scnprintf(text + len, sizeof(text) - len, ":%x",
+			 vnode->fid.unique);
 
 	if (size == 0)
 		return len;
-- 
2.24.0.rc1.363.gb1bccd3e3d-goog

Re: [PATCH] afs: xattr: use scnprintf

[Mark Salyzyn]

On 11/5/19 7:48 AM, Mark Salyzyn wrote:
> sprintf and snprintf are fragile in future maintenance, switch to
> using scnprintf to ensure no accidental Use After Free conditions
> are introduced.

Urrrk Out of band stack access ...

-- Mark