On Thu, Mar 11, 2021 at 10:10 AM David Howells <dhowells@xxxxxxxxxx> wrote:
>
> 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@xxxxxxxxxxxxxxxxxxx>
> Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
> Tested-by: Gaja Sophie Peters <gaja.peters@xxxxxxxxxxxxxxxxxxx>
> cc: linux-afs@xxxxxxxxxxxxxxxxxxx
> Link: http://lists.infradead.org/pipermail/linux-afs/2021-March/003498.html [1]
> ---
>
> fs/afs/fs_operation.c | 7 +++++--
> fs/afs/xattr.c | 8 +++++++-
> 2 files changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/fs/afs/fs_operation.c b/fs/afs/fs_operation.c
> index 97cab12b0a6c..71c58723763d 100644
> --- a/fs/afs/fs_operation.c
> +++ b/fs/afs/fs_operation.c
> @@ -181,10 +181,13 @@ void afs_wait_for_operation(struct afs_operation *op)
> 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) {
> diff --git a/fs/afs/xattr.c b/fs/afs/xattr.c
> index c629caae5002..4934e325a14a 100644
> --- a/fs/afs/xattr.c
> +++ b/fs/afs/xattr.c
> @@ -231,6 +231,8 @@ static int afs_xattr_get_yfs(const struct xattr_handler *handler,
> else
> ret = -ERANGE;
> }
> + } else if (ret == -ENOTSUPP) {
> + ret = -ENODATA;
> }
>
> error_yacl:
> @@ -256,6 +258,7 @@ static int afs_xattr_set_yfs(const struct xattr_handler *handler,
> {
> struct afs_operation *op;
> struct afs_vnode *vnode = AFS_FS_I(inode);
> + int ret;
>
> if (flags == XATTR_CREATE ||
> strcmp(name, "acl") != 0)
> @@ -270,7 +273,10 @@ static int afs_xattr_set_yfs(const struct xattr_handler *handler,
> 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 = {
Reviewed-by: Marc Dionne <marc.dionne@xxxxxxxxxxxx>
Marc
