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linux/fs/fuse/xattr.c
Jann Horn b18915248a fuse: use unsigned type for getxattr/listxattr size truncation
The existing code uses min_t(ssize_t, outarg.size, XATTR_LIST_MAX) when
parsing the FUSE daemon's response to a zero-length getxattr/listxattr
request.
On 32-bit kernels, where ssize_t and outarg.size are the same size, this is
wrong: The min_t() will pass through any size values that are negative when
interpreted as signed.
fuse_listxattr() will then return this userspace-supplied negative value,
which callers will treat as an error value.

This kind of bug pattern can lead to fairly bad security bugs because of
how error codes are used in the Linux kernel. If a caller were to convert
the numeric error into an error pointer, like so:

    struct foo *func(...) {
      int len = fuse_getxattr(..., NULL, 0);
      if (len < 0)
        return ERR_PTR(len);
      ...
    }

then it would end up returning this userspace-supplied negative value cast
to a pointer - but the caller of this function wouldn't recognize it as an
error pointer (IS_ERR_VALUE() only detects values in the narrow range in
which legitimate errno values are), and so it would just be treated as a
kernel pointer.

I think there is at least one theoretical codepath where this could happen,
but that path would involve virtio-fs with submounts plus some weird
SELinux configuration, so I think it's probably not a concern in practice.

Cc: stable@vger.kernel.org # v4.9
Fixes: 63401ccdb2 ("fuse: limit xattr returned size")
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
2024-08-28 18:10:29 +02:00

216 lines
5.0 KiB
C

/*
* FUSE: Filesystem in Userspace
* Copyright (C) 2001-2016 Miklos Szeredi <miklos@szeredi.hu>
*
* This program can be distributed under the terms of the GNU GPL.
* See the file COPYING.
*/
#include "fuse_i.h"
#include <linux/xattr.h>
#include <linux/posix_acl_xattr.h>
int fuse_setxattr(struct inode *inode, const char *name, const void *value,
size_t size, int flags, unsigned int extra_flags)
{
struct fuse_mount *fm = get_fuse_mount(inode);
FUSE_ARGS(args);
struct fuse_setxattr_in inarg;
int err;
if (fm->fc->no_setxattr)
return -EOPNOTSUPP;
memset(&inarg, 0, sizeof(inarg));
inarg.size = size;
inarg.flags = flags;
inarg.setxattr_flags = extra_flags;
args.opcode = FUSE_SETXATTR;
args.nodeid = get_node_id(inode);
args.in_numargs = 3;
args.in_args[0].size = fm->fc->setxattr_ext ?
sizeof(inarg) : FUSE_COMPAT_SETXATTR_IN_SIZE;
args.in_args[0].value = &inarg;
args.in_args[1].size = strlen(name) + 1;
args.in_args[1].value = name;
args.in_args[2].size = size;
args.in_args[2].value = value;
err = fuse_simple_request(fm, &args);
if (err == -ENOSYS) {
fm->fc->no_setxattr = 1;
err = -EOPNOTSUPP;
}
if (!err)
fuse_update_ctime(inode);
return err;
}
ssize_t fuse_getxattr(struct inode *inode, const char *name, void *value,
size_t size)
{
struct fuse_mount *fm = get_fuse_mount(inode);
FUSE_ARGS(args);
struct fuse_getxattr_in inarg;
struct fuse_getxattr_out outarg;
ssize_t ret;
if (fm->fc->no_getxattr)
return -EOPNOTSUPP;
memset(&inarg, 0, sizeof(inarg));
inarg.size = size;
args.opcode = FUSE_GETXATTR;
args.nodeid = get_node_id(inode);
args.in_numargs = 2;
args.in_args[0].size = sizeof(inarg);
args.in_args[0].value = &inarg;
args.in_args[1].size = strlen(name) + 1;
args.in_args[1].value = name;
/* This is really two different operations rolled into one */
args.out_numargs = 1;
if (size) {
args.out_argvar = true;
args.out_args[0].size = size;
args.out_args[0].value = value;
} else {
args.out_args[0].size = sizeof(outarg);
args.out_args[0].value = &outarg;
}
ret = fuse_simple_request(fm, &args);
if (!ret && !size)
ret = min_t(size_t, outarg.size, XATTR_SIZE_MAX);
if (ret == -ENOSYS) {
fm->fc->no_getxattr = 1;
ret = -EOPNOTSUPP;
}
return ret;
}
static int fuse_verify_xattr_list(char *list, size_t size)
{
size_t origsize = size;
while (size) {
size_t thislen = strnlen(list, size);
if (!thislen || thislen == size)
return -EIO;
size -= thislen + 1;
list += thislen + 1;
}
return origsize;
}
ssize_t fuse_listxattr(struct dentry *entry, char *list, size_t size)
{
struct inode *inode = d_inode(entry);
struct fuse_mount *fm = get_fuse_mount(inode);
FUSE_ARGS(args);
struct fuse_getxattr_in inarg;
struct fuse_getxattr_out outarg;
ssize_t ret;
if (fuse_is_bad(inode))
return -EIO;
if (!fuse_allow_current_process(fm->fc))
return -EACCES;
if (fm->fc->no_listxattr)
return -EOPNOTSUPP;
memset(&inarg, 0, sizeof(inarg));
inarg.size = size;
args.opcode = FUSE_LISTXATTR;
args.nodeid = get_node_id(inode);
args.in_numargs = 1;
args.in_args[0].size = sizeof(inarg);
args.in_args[0].value = &inarg;
/* This is really two different operations rolled into one */
args.out_numargs = 1;
if (size) {
args.out_argvar = true;
args.out_args[0].size = size;
args.out_args[0].value = list;
} else {
args.out_args[0].size = sizeof(outarg);
args.out_args[0].value = &outarg;
}
ret = fuse_simple_request(fm, &args);
if (!ret && !size)
ret = min_t(size_t, outarg.size, XATTR_LIST_MAX);
if (ret > 0 && size)
ret = fuse_verify_xattr_list(list, ret);
if (ret == -ENOSYS) {
fm->fc->no_listxattr = 1;
ret = -EOPNOTSUPP;
}
return ret;
}
int fuse_removexattr(struct inode *inode, const char *name)
{
struct fuse_mount *fm = get_fuse_mount(inode);
FUSE_ARGS(args);
int err;
if (fm->fc->no_removexattr)
return -EOPNOTSUPP;
args.opcode = FUSE_REMOVEXATTR;
args.nodeid = get_node_id(inode);
args.in_numargs = 1;
args.in_args[0].size = strlen(name) + 1;
args.in_args[0].value = name;
err = fuse_simple_request(fm, &args);
if (err == -ENOSYS) {
fm->fc->no_removexattr = 1;
err = -EOPNOTSUPP;
}
if (!err)
fuse_update_ctime(inode);
return err;
}
static int fuse_xattr_get(const struct xattr_handler *handler,
struct dentry *dentry, struct inode *inode,
const char *name, void *value, size_t size)
{
if (fuse_is_bad(inode))
return -EIO;
return fuse_getxattr(inode, name, value, size);
}
static int fuse_xattr_set(const struct xattr_handler *handler,
struct mnt_idmap *idmap,
struct dentry *dentry, struct inode *inode,
const char *name, const void *value, size_t size,
int flags)
{
if (fuse_is_bad(inode))
return -EIO;
if (!value)
return fuse_removexattr(inode, name);
return fuse_setxattr(inode, name, value, size, flags, 0);
}
static const struct xattr_handler fuse_xattr_handler = {
.prefix = "",
.get = fuse_xattr_get,
.set = fuse_xattr_set,
};
const struct xattr_handler * const fuse_xattr_handlers[] = {
&fuse_xattr_handler,
NULL
};