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From: Ronnie Sahlberg <lsahlber@redhat.com>
To: linux-cifs <linux-cifs@vger.kernel.org>
Cc: Ronnie Sahlberg <lsahlber@redhat.com>
Subject: [PATCH] cifs: make sure we do not overflow the max EA buffer size
Date: Thu, 13 Feb 2020 12:14:47 +1000
Message-ID: <20200213021447.24819-1-lsahlber@redhat.com> (raw)

RHBZ: 1752437

Before we add a new EA we should check that this will not overflow
the maximum buffer we have available to read the EAs back.
Otherwise we can get into a situation where the EAs are so big that
we can not read them back to the client and thus we can not list EAs
anymore or delete them.

Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
---
 fs/cifs/smb2ops.c | 35 ++++++++++++++++++++++++++++++++++-
 1 file changed, 34 insertions(+), 1 deletion(-)

diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c
index baa825f4cec0..3c76f69f4ca7 100644
--- a/fs/cifs/smb2ops.c
+++ b/fs/cifs/smb2ops.c
@@ -1116,7 +1116,8 @@ smb2_set_ea(const unsigned int xid, struct cifs_tcon *tcon,
 	void *data[1];
 	struct smb2_file_full_ea_info *ea = NULL;
 	struct kvec close_iov[1];
-	int rc;
+	struct smb2_query_info_rsp *rsp;
+	int rc, used_len = 0;
 
 	if (smb3_encryption_required(tcon))
 		flags |= CIFS_TRANSFORM_REQ;
@@ -1139,6 +1140,38 @@ smb2_set_ea(const unsigned int xid, struct cifs_tcon *tcon,
 							     cifs_sb);
 			if (rc == -ENODATA)
 				goto sea_exit;
+		} else {
+			/* If we are adding a attribute we should first check
+			 * if there will be enough space available to store
+			 * the new EA. If not we should not add it since we
+			 * would not be able to even read the EAs back.
+			 */
+			rc = smb2_query_info_compound(xid, tcon, utf16_path,
+				      FILE_READ_EA,
+				      FILE_FULL_EA_INFORMATION,
+				      SMB2_O_INFO_FILE,
+				      CIFSMaxBufSize -
+				      MAX_SMB2_CREATE_RESPONSE_SIZE -
+				      MAX_SMB2_CLOSE_RESPONSE_SIZE,
+				      &rsp_iov[1], &resp_buftype[1], cifs_sb);
+			if (rc == 0) {
+				rsp = (struct smb2_query_info_rsp *)rsp_iov[1].iov_base;
+				used_len = rsp->OutputBufferLength;
+			}
+			free_rsp_buf(resp_buftype[1], rsp_iov[1].iov_base);
+			resp_buftype[1] = CIFS_NO_BUFFER;
+			memset(&rsp_iov[1], 0, sizeof(rsp_iov[1]));
+			rc = 0;
+
+			/* Use a fudge factor of 256 bytes in case we collide
+			 * with a different set_EAs command.
+			 */
+			if(CIFSMaxBufSize - MAX_SMB2_CREATE_RESPONSE_SIZE -
+			   MAX_SMB2_CLOSE_RESPONSE_SIZE - 256 <
+			   used_len + ea_name_len + ea_value_len + 1) {
+				rc = -ENOSPC;
+				goto sea_exit;
+			}
 		}
 	}
 
-- 
2.13.6


             reply index

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-13  2:14 Ronnie Sahlberg [this message]
2020-02-14  6:14 ` Steve French
2020-02-14 19:04   ` Pavel Shilovsky

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