linux-kernel - [PATCH 5.15 269/317] NFSv4.2: fix listxattr maximum XDR buffer size

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Message-ID: <20240324233458.1352854-270-sashal@kernel.org>
Date: Sun, 24 Mar 2024 19:34:09 -0400
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: Jorge Mora <jmora1300@...il.com>,
	Jorge Mora <mora@...app.com>,
	Benjamin Coddington <bcodding@...hat.com>,
	Trond Myklebust <trond.myklebust@...merspace.com>,
	Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.15 269/317] NFSv4.2: fix listxattr maximum XDR buffer size

From: Jorge Mora <jmora1300@...il.com>

[ Upstream commit bcac8bff90a6ee1629f90669cdb9d28fb86049b0 ]

Switch order of operations to avoid creating a short XDR buffer:
e.g., buflen = 12, old xdrlen = 12, new xdrlen = 20.

Having a short XDR buffer leads to lxa_maxcount be a few bytes
less than what is needed to retrieve the whole list when using
a buflen as returned by a call with size = 0:
    buflen = listxattr(path, NULL, 0);
    buf = malloc(buflen);
    buflen = listxattr(path, buf, buflen);

For a file with one attribute (name = '123456'), the first call
with size = 0 will return buflen = 12 ('user.123456\x00').
The second call with size = 12, sends LISTXATTRS with
lxa_maxcount = 12 + 8 (cookie) + 4 (array count) = 24. The
XDR buffer needs 8 (cookie) + 4 (array count) + 4 (name count)
+ 6 (name len) + 2 (padding) + 4 (eof) = 28 which is 4 bytes
shorter than the lxa_maxcount provided in the call.

Fixes: 04a5da690e8f ("NFSv4.2: define limits and sizes for user xattr handling")
Signed-off-by: Jorge Mora <mora@...app.com>
Reviewed-by: Benjamin Coddington <bcodding@...hat.com>
Signed-off-by: Trond Myklebust <trond.myklebust@...merspace.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 fs/nfs/nfs42.h | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/fs/nfs/nfs42.h b/fs/nfs/nfs42.h
index 0fe5aacbcfdf1..e7192d0eea3de 100644
--- a/fs/nfs/nfs42.h
+++ b/fs/nfs/nfs42.h
@@ -54,11 +54,14 @@ int nfs42_proc_removexattr(struct inode *inode, const char *name);
  * They would be 7 bytes long in the eventual buffer ("user.x\0"), and
  * 8 bytes long XDR-encoded.
  *
- * Include the trailing eof word as well.
+ * Include the trailing eof word as well and make the result a multiple
+ * of 4 bytes.
  */
 static inline u32 nfs42_listxattr_xdrsize(u32 buflen)
 {
-	return ((buflen / (XATTR_USER_PREFIX_LEN + 2)) * 8) + 4;
+	u32 size = 8 * buflen / (XATTR_USER_PREFIX_LEN + 2) + 4;
+
+	return (size + 3) & ~3;
 }
 #endif /* CONFIG_NFS_V4_2 */
 #endif /* __LINUX_FS_NFS_NFS4_2_H */
-- 
2.43.0