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9pfs: local: lgetxattr: don't follow symlinks

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The local_lgetxattr() callback is vulnerable to symlink attacks because
it calls lgetxattr() which follows symbolic links in all path elements but
the rightmost one.

This patch introduces a helper to emulate the non-existing fgetxattrat()
function: it is implemented with /proc/self/fd which provides a trusted
path that can be safely passed to lgetxattr().

local_lgetxattr() is converted to use this helper and opendir_nofollow().

This partly fixes CVE-2016-9602.

Signed-off-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Greg Kurz 2017-02-26 23:42:26 +01:00
parent 996a0d76d7
commit 56ad3e54da
6 changed files with 43 additions and 28 deletions
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31
hw/9pfs/9p-xattr.c
View file

@ -15,6 +15,8 @@
#include "9p.h"
#include "fsdev/file-op-9p.h"
#include "9p-xattr.h"
#include "9p-util.h"
#include "9p-local.h"
static XattrOperations *get_xattr_operations(XattrOperations **h,
@ -143,16 +145,31 @@ int v9fs_remove_xattr(FsContext *ctx,
}
ssize_t local_getxattr_nofollow(FsContext *ctx, const char *path,
const char *name, void *value, size_t size)
{
char *dirpath = g_path_get_dirname(path);
char *filename = g_path_get_basename(path);
int dirfd;
ssize_t ret = -1;
dirfd = local_opendir_nofollow(ctx, dirpath);
if (dirfd == -1) {
goto out;
}
ret = fgetxattrat_nofollow(dirfd, filename, name, value, size);
close_preserve_errno(dirfd);
out:
g_free(dirpath);
g_free(filename);
return ret;
}
ssize_t pt_getxattr(FsContext *ctx, const char *path, const char *name,
void *value, size_t size)
{
char *buffer;
ssize_t ret;
buffer = rpath(ctx, path);
ret = lgetxattr(buffer, name, value, size);
g_free(buffer);
return ret;
return local_getxattr_nofollow(ctx, path, name, value, size);
}
int pt_setxattr(FsContext *ctx, const char *path, const char *name, void *value,