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

The local_utimensat() callback is vulnerable to symlink attacks because it
calls qemu_utimens()->utimensat(AT_SYMLINK_NOFOLLOW) which follows symbolic
links in all path elements but the rightmost one or qemu_utimens()->utimes()
which follows symbolic links for all path elements.

This patch converts local_utimensat() to rely on opendir_nofollow() and
utimensat(AT_SYMLINK_NOFOLLOW) directly instead of using qemu_utimens().
It is hence assumed that the OS supports utimensat(), i.e. has glibc 2.6
or higher and linux 2.6.22 or higher, which seems reasonable nowadays.

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 23:43:17 +01:00
parent a0e640a872
commit a33eda0dd9
1 changed files with 13 additions and 6 deletions
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19
hw/9pfs/9p-local.c
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@ -959,13 +959,20 @@ static int local_chown(FsContext *fs_ctx, V9fsPath *fs_path, FsCred *credp)
static int local_utimensat(FsContext *s, V9fsPath *fs_path,
const struct timespec *buf)
{
char *buffer;
int ret;
char *path = fs_path->data;
char *dirpath = g_path_get_dirname(fs_path->data);
char *name = g_path_get_basename(fs_path->data);
int dirfd, ret = -1;
buffer = rpath(s, path);
ret = qemu_utimens(buffer, buf);
g_free(buffer);
dirfd = local_opendir_nofollow(s, dirpath);
if (dirfd == -1) {
goto out;
}
ret = utimensat(dirfd, name, buf, AT_SYMLINK_NOFOLLOW);
close_preserve_errno(dirfd);
out:
g_free(dirpath);
g_free(name);
return ret;
}