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

Sasha Levin
2024-03-24T23:39:22Z

From: Jorge Mora <jmora1300@gmail.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@netapp.com>
Reviewed-by: Benjamin Coddington <bcodding@redhat.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Sasha Levin <sashal@kernel.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