Truncate directory cookies to 31 bits to avoid problems exposed in Linux
binaries which cast the returned values to 64-bits and fail due to sign expansion. More details are provided in the big comment in tmpfs.h that describes how the new tmpfs_dircookie works. This is a rather ugly hack that shall be fixed with a cleaner solution, but this resolves the problem in an effective way. Fixes kern PR/32034.
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jmmv
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@ -1,4 +1,4 @@
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/* $NetBSD: tmpfs.h,v 1.21 2006/07/23 22:06:10 ad Exp $ */
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/* $NetBSD: tmpfs.h,v 1.22 2006/11/05 16:59:18 jmmv Exp $ */
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/*
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* Copyright (c) 2005, 2006 The NetBSD Foundation, Inc.
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@ -87,10 +87,71 @@ struct tmpfs_dirent {
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* importantly, to remove redundancy. */
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TAILQ_HEAD(tmpfs_dir, tmpfs_dirent);
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#define TMPFS_DIRCOOKIE(dirent) ((off_t)(uintptr_t)(dirent))
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/* Each entry in a directory has a cookie that identifies it. Cookies
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* supersede offsets within directories because, given how tmpfs stores
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* directories in memory, there is no such thing as an offset. (Emulating
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* a real offset could be very difficult.)
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*
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* The '.', '..' and the end of directory markers have fixed cookies which
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* cannot collide with the cookies generated by other entries. The cookies
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* fot the other entries are generated based on the memory address on which
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* stores their information is stored.
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*
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* Ideally, using the entry's memory pointer as the cookie would be enough
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* to represent it and it wouldn't cause collisions in any system.
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* Unfortunately, this results in "offsets" with very large values which
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* later raise problems in the Linux compatibility layer (and maybe in other
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* places) as described in PR kern/32034. Hence we need to workaround this
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* with a rather ugly hack.
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*
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* Linux 32-bit binaries, unless built with _FILE_OFFSET_BITS=64, have off_t
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* set to 'long', which is a 32-bit *signed* long integer. Regardless of
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* the macro value, GLIBC (2.3 at least) always uses the getdents64
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* system call (when calling readdir) which internally returns off64_t
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* offsets. In order to make 32-bit binaries work, *GLIBC* converts the
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* 64-bit values returned by the kernel to 32-bit ones and aborts with
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* EOVERFLOW if the conversion results in values that won't fit in 32-bit
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* integers (which it assumes is because the directory is extremely large).
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* This wouldn't cause problems if we were dealing with unsigned integers,
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* but as we have signed integers, this check fails due to sign expansion.
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*
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* For example, consider that the kernel returns the 0xc1234567 cookie to
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* userspace in a off64_t integer. Later on, GLIBC casts this value to
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* off_t (remember, signed) with code similar to:
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* system call returns the offset in kernel_value;
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* off_t casted_value = kernel_value;
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* if (sizeof(off_t) != sizeof(off64_t) &&
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* kernel_value != casted_value)
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* error!
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* In this case, casted_value still has 0xc1234567, but when it is compared
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* for equality against kernel_value, it is promoted to a 64-bit integer and
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* becomes 0xffffffffc1234567, which is different than 0x00000000c1234567.
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* Then, GLIBC assumes this is because the directory is very large.
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*
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* Given that all the above happens in user-space, we have no control over
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* it; therefore we must workaround the issue here. We do this by
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* truncating the pointer value to a 32-bit integer and hope that there
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* won't be collisions. In fact, this will not cause any problems in
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* 32-bit platforms but some might arise in 64-bit machines (I'm not sure
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* if they can happen at all in practice).
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*
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* XXX A nicer solution shall be attempted. */
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#define TMPFS_DIRCOOKIE_DOT 0
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#define TMPFS_DIRCOOKIE_DOTDOT 1
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#define TMPFS_DIRCOOKIE_EOF 2
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static __inline
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off_t
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tmpfs_dircookie(struct tmpfs_dirent *de)
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{
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off_t cookie;
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cookie = ((off_t)(uintptr_t)de >> 1) & 0x7FFFFFFF;
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KASSERT(cookie != TMPFS_DIRCOOKIE_DOT);
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KASSERT(cookie != TMPFS_DIRCOOKIE_DOTDOT);
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KASSERT(cookie != TMPFS_DIRCOOKIE_EOF);
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return cookie;
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}
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/* --------------------------------------------------------------------- */
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@ -364,7 +425,7 @@ int tmpfs_truncate(struct vnode *, off_t);
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KASSERT((node)->tn_type == VDIR); \
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KASSERT((node)->tn_size % sizeof(struct tmpfs_dirent) == 0); \
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KASSERT((node)->tn_spec.tn_dir.tn_readdir_lastp == NULL || \
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TMPFS_DIRCOOKIE((node)->tn_spec.tn_dir.tn_readdir_lastp) == \
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tmpfs_dircookie((node)->tn_spec.tn_dir.tn_readdir_lastp) == \
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(node)->tn_spec.tn_dir.tn_readdir_lastn);
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/* --------------------------------------------------------------------- */
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@ -1,4 +1,4 @@
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/* $NetBSD: tmpfs_subr.c,v 1.26 2006/10/30 15:11:01 jmmv Exp $ */
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/* $NetBSD: tmpfs_subr.c,v 1.27 2006/11/05 16:59:18 jmmv Exp $ */
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/*
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* Copyright (c) 2005, 2006 The NetBSD Foundation, Inc.
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@ -42,7 +42,7 @@
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*/
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#include <sys/cdefs.h>
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__KERNEL_RCSID(0, "$NetBSD: tmpfs_subr.c,v 1.26 2006/10/30 15:11:01 jmmv Exp $");
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__KERNEL_RCSID(0, "$NetBSD: tmpfs_subr.c,v 1.27 2006/11/05 16:59:18 jmmv Exp $");
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#include <sys/param.h>
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#include <sys/dirent.h>
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@ -695,7 +695,7 @@ tmpfs_dir_getdotdotdent(struct tmpfs_node *node, struct uio *uio)
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if (de == NULL)
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uio->uio_offset = TMPFS_DIRCOOKIE_EOF;
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else
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uio->uio_offset = TMPFS_DIRCOOKIE(de);
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uio->uio_offset = tmpfs_dircookie(de);
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}
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}
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@ -720,7 +720,7 @@ tmpfs_dir_lookupbycookie(struct tmpfs_node *node, off_t cookie)
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}
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TAILQ_FOREACH(de, &node->tn_spec.tn_dir.tn_dir, td_entries) {
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if (TMPFS_DIRCOOKIE(de) == cookie) {
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if (tmpfs_dircookie(de) == cookie) {
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break;
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}
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}
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@ -829,7 +829,7 @@ tmpfs_dir_getdents(struct tmpfs_node *node, struct uio *uio, off_t *cntp)
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node->tn_spec.tn_dir.tn_readdir_lastp = NULL;
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} else {
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node->tn_spec.tn_dir.tn_readdir_lastn = uio->uio_offset =
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TMPFS_DIRCOOKIE(de);
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tmpfs_dircookie(de);
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node->tn_spec.tn_dir.tn_readdir_lastp = de;
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}
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@ -1,4 +1,4 @@
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/* $NetBSD: tmpfs_vnops.c,v 1.28 2006/11/02 15:35:25 jmmv Exp $ */
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/* $NetBSD: tmpfs_vnops.c,v 1.29 2006/11/05 16:59:18 jmmv Exp $ */
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/*
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* Copyright (c) 2005, 2006 The NetBSD Foundation, Inc.
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@ -42,7 +42,7 @@
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*/
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#include <sys/cdefs.h>
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__KERNEL_RCSID(0, "$NetBSD: tmpfs_vnops.c,v 1.28 2006/11/02 15:35:25 jmmv Exp $");
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__KERNEL_RCSID(0, "$NetBSD: tmpfs_vnops.c,v 1.29 2006/11/05 16:59:18 jmmv Exp $");
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#include <sys/param.h>
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#include <sys/dirent.h>
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@ -1179,7 +1179,7 @@ outok:
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if (de == NULL) {
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off = TMPFS_DIRCOOKIE_EOF;
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} else {
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off = TMPFS_DIRCOOKIE(de);
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off = tmpfs_dircookie(de);
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}
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}
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