[PATCH 5.10 033/157] afs: Fix accessing YFS xattrs on a non-YFS server

Greg Kroah-Hartman
2021-03-22T12:46:42Z

From: David Howells <dhowells@redhat.com>

commit 64fcbb6158ecc684d84c64424830a9c37c77c5b9 upstream.

If someone attempts to access YFS-related xattrs (e.g. afs.yfs.acl) on a
file on a non-YFS AFS server (such as OpenAFS), then the kernel will jump
to a NULL function pointer because the afs_fetch_acl_operation descriptor
doesn't point to a function for issuing an operation on a non-YFS
server[1].

Fix this by making afs_wait_for_operation() check that the issue_afs_rpc
method is set before jumping to it and setting -ENOTSUPP if not. This fix
also covers other potential operations that also only exist on YFS servers.

afs_xattr_get/set_yfs() then need to translate -ENOTSUPP to -ENODATA as the
former error is internal to the kernel.

The bug shows up as an oops like the following:

BUG: kernel NULL pointer dereference, address: 0000000000000000
[...]
Code: Unable to access opcode bytes at RIP 0xffffffffffffffd6.
[...]
Call Trace:
afs_wait_for_operation+0x83/0x1b0 [kafs]
afs_xattr_get_yfs+0xe6/0x270 [kafs]
__vfs_getxattr+0x59/0x80
vfs_getxattr+0x11c/0x140
getxattr+0x181/0x250
? __check_object_size+0x13f/0x150
? __fput+0x16d/0x250
__x64_sys_fgetxattr+0x64/0xb0
do_syscall_64+0x49/0xc0
entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x7fb120a9defe

This was triggered with "cp -a" which attempts to copy xattrs, including
afs ones, but is easier to reproduce with getfattr, e.g.:

getfattr -d -m ".*" /afs/openafs.org/

Fixes: e49c7b2f6de7 ("afs: Build an abstraction around an "operation" concept")
Reported-by: Gaja Sophie Peters <gaja.peters@math.uni-hamburg.de>
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-by: Gaja Sophie Peters <gaja.peters@math.uni-hamburg.de>
Reviewed-by: Marc Dionne <marc.dionne@auristor.com>
Reviewed-by: Jeffrey Altman <jaltman@auristor.com>
cc: linux-afs@lists.infradead.org
Link: http://lists.infradead.org/pipermail/linux-afs/2021-March/003498.html [1]
Link: http://lists.infradead.org/pipermail/linux-afs/2021-March/003566.html # v1
Link: http://lists.infradead.org/pipermail/linux-afs/2021-March/003572.html # v2
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/afs/fs_operation.c | 7 +++++--
fs/afs/xattr.c | 8 +++++++-
2 files changed, 12 insertions(+), 3 deletions(-)

--- a/fs/afs/fs_operation.c
+++ b/fs/afs/fs_operation.c
@@ -181,10 +181,13 @@ void afs_wait_for_operation(struct afs_o
if (test_bit(AFS_SERVER_FL_IS_YFS, &op->server->flags) &&
op->ops->issue_yfs_rpc)
op->ops->issue_yfs_rpc(op);
- else
+ else if (op->ops->issue_afs_rpc)
op->ops->issue_afs_rpc(op);
+ else
+ op->ac.error = -ENOTSUPP;

- op->error = afs_wait_for_call_to_complete(op->call, &op->ac);
+ if (op->call)
+ op->error = afs_wait_for_call_to_complete(op->call, &op->ac);
}

switch (op->error) {
--- a/fs/afs/xattr.c
+++ b/fs/afs/xattr.c
@@ -230,6 +230,8 @@ static int afs_xattr_get_yfs(const struc
else
ret = -ERANGE;
}
+ } else if (ret == -ENOTSUPP) {
+ ret = -ENODATA;
}

error_yacl:
@@ -254,6 +256,7 @@ static int afs_xattr_set_yfs(const struc
{
struct afs_operation *op;
struct afs_vnode *vnode = AFS_FS_I(inode);
+ int ret;

if (flags == XATTR_CREATE ||
strcmp(name, "acl") != 0)
@@ -268,7 +271,10 @@ static int afs_xattr_set_yfs(const struc
return afs_put_operation(op);

op->ops = &yfs_store_opaque_acl2_operation;
- return afs_do_sync_operation(op);
+ ret = afs_do_sync_operation(op);
+ if (ret == -ENOTSUPP)
+ ret = -ENODATA;
+ return ret;
}

static const struct xattr_handler afs_xattr_yfs_handler = {