Package: dpkg
Version: 1.21.22
Severity: wishlist
Dear Maintainer,
I'm working on the dpkg codebase, and I've found that when extracting a
.deb with an uncompressed data.tar, we can install it even without calling
dpk-deb as subprocess.
Find a patch attached.
Regards,
-- Package-specific info:
This system uses merged-usr-via-aliased-dirs, going behind dpkg's
back, breaking its core assumptions. This can cause silent file
overwrites and disappearances, and its general tools misbehavior.
See <https://wiki.debian.org/Teams/Dpkg/FAQ#broken-usrmerge>.
-- System Information:
Debian Release: 12.7
APT prefers stable-security
APT policy: (500, 'stable-security'), (500, 'stable')
Architecture: amd64 (x86_64)
Kernel: Linux 6.11.0-saturno (SMP w/8 CPU threads)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), LANGUAGE not set
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
Versions of packages dpkg depends on:
ii libbz2-1.0 1.0.8-5+b1
ii libc6 2.36-9+deb12u8
ii liblzma5 5.4.1-0.2
ii libmd0 1.0.4-2
ii libselinux1 3.4-1+b6
ii libzstd1 1.5.4+dfsg2-5
ii tar 1.34+dfsg-1.2+deb12u1
ii zlib1g 1:1.2.13.dfsg-1
dpkg recommends no packages.
Versions of packages dpkg suggests:
ii apt 2.6.1
pn debsig-verify <none>
-- no debconf information
From 608ecaee805e7b5305e3b527c5109652908c4d5b Mon Sep 17 00:00:00 2001
From: Matteo Croce <teknora...@meta.com>
Date: Tue, 22 Oct 2024 02:05:32 +0200
Subject: [PATCH] dpkg: don't spawn a subprocess if not needed
If the archive is uncompressed, avoid execing `deb-src`, just open the
file and seek to the data start.
read_line() is just moved from src/deb/extract.c to lib/dpkg/ar.c.
dpkg_ar_member_get_offset() is a new function which returns the offset
of data.tar inside the deb archive.
If dpkg_ar_member_get_offset() returns a valid offset, and the archive
is not compressed, just open the archive, skip to the data.tar
start and pass that file descriptor to tar_extractor(), without
spawning a subprocess and a pipe.
---
lib/dpkg/ar.c | 74 +++++++++++++++++++++++++++++++++++++++++++++++
lib/dpkg/ar.h | 3 ++
src/deb/extract.c | 29 -------------------
src/main/unpack.c | 46 +++++++++++++++++++----------
4 files changed, 107 insertions(+), 45 deletions(-)
diff --git a/lib/dpkg/ar.c b/lib/dpkg/ar.c
index 6eea5ad13..8388ed90b 100644
--- a/lib/dpkg/ar.c
+++ b/lib/dpkg/ar.c
@@ -232,3 +232,77 @@ dpkg_ar_member_put_file(struct dpkg_ar *ar,
if (fd_write(ar->fd, "\n", 1) < 0)
ohshite(_("unable to write file '%s'"), ar->name);
}
+
+ssize_t read_line(int fd, char *buf, size_t min_size, size_t max_size)
+{
+ ssize_t line_size = 0;
+ size_t n = min_size;
+
+ while (line_size < (ssize_t) max_size) {
+ ssize_t nread;
+ char *nl;
+
+ nread = fd_read(fd, buf + line_size, n);
+ if (nread <= 0)
+ return nread;
+
+ nl = memchr(buf + line_size, '\n', nread);
+ line_size += nread;
+
+ if (nl != NULL) {
+ nl[1] = '\0';
+ return line_size;
+ }
+
+ n = 1;
+ }
+
+ buf[line_size] = '\0';
+ return line_size;
+}
+
+off_t dpkg_ar_member_get_offset(const char *debar)
+{
+ struct dpkg_ar ar = { .name = debar };
+ char versionbuf[sizeof(DPKG_AR_MAGIC)];
+ off_t memberlen;
+ ssize_t rc;
+ off_t offset = -1;
+
+ ar.fd = open(ar.name, O_RDONLY);
+ if (ar.fd < 0)
+ ohshite(_("failed to open archive '%.255s'"), debar);
+
+ rc = read_line(ar.fd, versionbuf, sizeof(DPKG_AR_MAGIC) - 1,
+ sizeof(versionbuf));
+ if (rc <= 0)
+ ohshite(_("read failed"));
+ if (strcmp(versionbuf, DPKG_AR_MAGIC))
+ ohshite(_("archive magic version number"));
+
+ for (;;) {
+ struct dpkg_ar_hdr arh;
+
+ rc = read(ar.fd, &arh, sizeof(arh));
+ if (rc != sizeof(arh))
+ break;
+
+ if (dpkg_ar_member_is_illegal(&arh))
+ ohshite(_("file '%.250s' is corrupt - bad archive
header magic"),
+ debar);
+
+ dpkg_ar_normalize_name(&arh);
+ if (strcmp(arh.ar_name, "data.tar") == 0) {
+ offset = lseek(ar.fd, 0, SEEK_CUR);
+ break;
+ }
+
+ memberlen = dpkg_ar_member_get_size(&ar, &arh);
+ if (memberlen % 2)
+ memberlen++;
+ lseek(ar.fd, memberlen, SEEK_CUR);
+ }
+
+ close(ar.fd);
+ return offset;
+}
diff --git a/lib/dpkg/ar.h b/lib/dpkg/ar.h
index 8a7aff977..3af7fbe89 100644
--- a/lib/dpkg/ar.h
+++ b/lib/dpkg/ar.h
@@ -76,6 +76,8 @@ struct dpkg_ar_member {
gid_t gid;
};
+ssize_t read_line(int fd, char *buf, size_t min_size, size_t max_size);
+
struct dpkg_ar *
dpkg_ar_fdopen(const char *filename, int fd);
struct dpkg_ar *dpkg_ar_open(const char *filename);
@@ -95,6 +97,7 @@ void dpkg_ar_member_put_mem(struct dpkg_ar *ar, const char
*name,
const void *data, size_t size);
off_t dpkg_ar_member_get_size(struct dpkg_ar *ar, struct dpkg_ar_hdr *arh);
+off_t dpkg_ar_member_get_offset(const char *debar);
/** @} */
DPKG_END_DECLS
diff --git a/src/deb/extract.c b/src/deb/extract.c
index 08b281564..b76e0160a 100644
--- a/src/deb/extract.c
+++ b/src/deb/extract.c
@@ -74,35 +74,6 @@ read_fail(int rc, const char *filename, const char *what)
ohshite(_("error reading %s from file %.255s"), what, filename);
}
-static ssize_t
-read_line(int fd, char *buf, size_t min_size, size_t max_size)
-{
- ssize_t line_size = 0;
- size_t n = min_size;
-
- while (line_size < (ssize_t)max_size) {
- ssize_t nread;
- char *nl;
-
- nread = fd_read(fd, buf + line_size, n);
- if (nread <= 0)
- return nread;
-
- nl = memchr(buf + line_size, '\n', nread);
- line_size += nread;
-
- if (nl != NULL) {
- nl[1] = '\0';
- return line_size;
- }
-
- n = 1;
- }
-
- buf[line_size] = '\0';
- return line_size;
-}
-
void
extracthalf(const char *debar, const char *dir,
enum dpkg_tar_options taroption, int admininfo)
diff --git a/src/main/unpack.c b/src/main/unpack.c
index e57a6e35e..9ae5959e7 100644
--- a/src/main/unpack.c
+++ b/src/main/unpack.c
@@ -55,6 +55,7 @@
#include <dpkg/db-ctrl.h>
#include <dpkg/db-fsys.h>
#include <dpkg/triglib.h>
+#include <dpkg/ar.h>
#include "file-match.h"
#include "main.h"
@@ -1223,6 +1224,7 @@ void process_archive(const char *filename) {
const char *pfilename;
struct fsys_namenode_queue newconffiles, newfiles_queue;
struct stat stab;
+ off_t data_tar_offset;
cleanup_pkg_failed= cleanup_conflictor_failed= 0;
@@ -1536,24 +1538,33 @@ void process_archive(const char *filename) {
* files get replaced ‘as we go’.
*/
- m_pipe(p1);
- push_cleanup(cu_closepipe, ehflag_bombout, 1, (void *)&p1[0]);
- pid = subproc_fork();
- if (pid == 0) {
- m_dup2(p1[1],1); close(p1[0]); close(p1[1]);
- execlp(BACKEND, BACKEND, "--fsys-tarfile", filename, NULL);
- ohshite(_("unable to execute %s (%s)"),
- _("package filesystem archive extraction"), BACKEND);
+ data_tar_offset = dpkg_ar_member_get_offset(filename);
+
+ if (data_tar_offset < 0) {
+ m_pipe(p1);
+ push_cleanup(cu_closepipe, ehflag_bombout, 1, (void *)&p1[0]);
+ pid = subproc_fork();
+ if (pid == 0) {
+ m_dup2(p1[1],1); close(p1[0]); close(p1[1]);
+ execlp(BACKEND, BACKEND, "--fsys-tarfile", filename, NULL);
+ ohshite(_("unable to execute %s (%s)"),
+ _("package filesystem archive extraction"), BACKEND);
+ }
+ close(p1[1]);
+ p1[1] = -1;
}
- close(p1[1]);
- p1[1] = -1;
newfiles_queue.head = NULL;
newfiles_queue.tail = &newfiles_queue.head;
tc.newfiles_queue = &newfiles_queue;
push_cleanup(cu_fileslist, ~0, 0);
tc.pkg= pkg;
- tc.backendpipe= p1[0];
+ if (data_tar_offset < 0) {
+ tc.backendpipe= p1[0];
+ } else {
+ tc.backendpipe= open(filename, O_RDONLY);
+ lseek(tc.backendpipe, data_tar_offset, SEEK_SET);
+ }
tc.pkgset_getting_in_sync = pkgset_getting_in_sync(pkg);
/* Setup the tar archive. */
@@ -1565,11 +1576,14 @@ void process_archive(const char *filename) {
if (rc)
dpkg_error_print(&tar.err,
_("corrupted filesystem tarfile in package archive"));
- if (fd_skip(p1[0], -1, &err) < 0)
- ohshit(_("cannot zap possible trailing zeros from dpkg-deb: %s"), err.str);
- close(p1[0]);
- p1[0] = -1;
- subproc_reap(pid, BACKEND " --fsys-tarfile", SUBPROC_NOPIPE);
+
+ if (data_tar_offset < 0) {
+ if (fd_skip(p1[0], -1, &err) < 0)
+ ohshit(_("cannot zap possible trailing zeros from dpkg-deb: %s"),
err.str);
+ close(p1[0]);
+ p1[0] = -1;
+ subproc_reap(pid, BACKEND " --fsys-tarfile", SUBPROC_NOPIPE);
+ }
tar_deferred_extract(newfiles_queue.head, pkg);
--
2.39.5
