[hackers] [sbase][PATCH] tar: support creating entries with long paths and link targets.

From: Andrew Chambers <ac_AT_acha.ninja>
Date: Mon, 2 May 2022 00:25:18 +1200

Posix tarballs use extended headers to represent paths that do
not fit in the original ustar header format. This patch implements
the transparent creation of these headers when paths overflow.

---
 tar.c | 81 +++++++++++++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 71 insertions(+), 10 deletions(-)
diff --git a/tar.c b/tar.c
index d3a9f3b..f46b5be 100644
--- a/tar.c
+++ b/tar.c
_AT_@ -176,17 +176,51 @@ putoctal(char *dst, unsigned num, int size)
 		eprintf("snprintf: input number too large\n");
 }
 
+static void
+fillchksum(struct header *h)
+{
+	char *b;
+	size_t i, chksum;
+
+	b = (char *)h;
+	memset(h->chksum, ' ', sizeof(h->chksum));
+	for (i = 0, chksum = 0; i < sizeof(*h); i++)
+		chksum += (unsigned char)b[i];
+	putoctal(h->chksum, chksum, sizeof(h->chksum));
+}
+
+static size_t
+xhdradd(char xhdr[], size_t max, const char *k, const char *v, size_t vlen)
+{
+	size_t sz, prevsz;
+
+	/* The size of the message includes itself, so compute it via iteration. */
+	prevsz = max;
+	while (1) {
+		sz = snprintf(xhdr, max, "%ld %s=%.*s\n", prevsz, k, (int)vlen, v);
+		if (sz == max)
+			eprintf("pax headers too large\n");
+		if (sz == prevsz)
+			return sz;
+		prevsz = sz;
+	}
+}
+
 static int
 archive(const char *path)
 {
 	char b[BLKSIZ];
+	char xb[BLKSIZ];
+	char xhdr[8192];
+	char link[4096];
 	struct group *gr;
-	struct header *h;
+	struct header *h, *xh;
 	struct passwd *pw;
 	struct stat st;
-	size_t chksum, i;
+	size_t xhdroffset, pathlen;
 	ssize_t l, r;
 	int fd = -1;
+	xhdroffset = 0;
 
 	if (lstat(path, &st) < 0) {
 		weprintf("lstat %s:", path);
_AT_@ -201,7 +235,7 @@ archive(const char *path)
 
 	h = (struct header *)b;
 	memset(b, 0, sizeof(b));
-	estrlcpy(h->name,    path,                        sizeof(h->name));
+	strncpy (h->name,    path,                        sizeof(h->name));
 	putoctal(h->mode,    (unsigned)st.st_mode & 0777, sizeof(h->mode));
 	putoctal(h->uid,     (unsigned)st.st_uid,         sizeof(h->uid));
 	putoctal(h->gid,     (unsigned)st.st_gid,         sizeof(h->gid));
_AT_@ -212,6 +246,12 @@ archive(const char *path)
 	estrlcpy(h->uname,   pw ? pw->pw_name : "",       sizeof(h->uname));
 	estrlcpy(h->gname,   gr ? gr->gr_name : "",       sizeof(h->gname));
 
+	h->name[sizeof(h->name)-1] = 0;
+	pathlen = strlen(path);
+	if (pathlen >= sizeof(h->name)) {
+		xhdroffset += xhdradd(&xhdr[xhdroffset], sizeof(xhdr)-xhdroffset, "path", path, pathlen);
+	}
+
 	if (S_ISREG(st.st_mode)) {
 		h->type = REG;
 		putoctal(h->size, (unsigned)st.st_size,  sizeof(h->size));
_AT_@ -222,9 +262,16 @@ archive(const char *path)
 		h->type = DIRECTORY;
 	} else if (S_ISLNK(st.st_mode)) {
 		h->type = SYMLINK;
-		if ((r = readlink(path, h->linkname, sizeof(h->linkname) - 1)) < 0)
+		if ((r = readlink(path, link, sizeof(link) - 1)) < 0)
 			eprintf("readlink %s:", path);
-		h->linkname[r] = '\0';
+		if (r == sizeof(link))
+			eprintf("link target too long\n");
+		link[r] = '\0';
+		strncpy(h->linkname, link, sizeof(h->linkname));
+		h->linkname[sizeof(h->linkname)-1] = 0;
+		if (r >= sizeof(h->linkname)) {
+			xhdroffset += xhdradd(&xhdr[xhdroffset], sizeof(xhdr)-xhdroffset, "linkpath", link, r);
+		}
 	} else if (S_ISCHR(st.st_mode) || S_ISBLK(st.st_mode)) {
 		h->type = S_ISCHR(st.st_mode) ? CHARDEV : BLOCKDEV;
 		putoctal(h->major, (unsigned)major(st.st_dev), sizeof(h->major));
_AT_@ -233,10 +280,24 @@ archive(const char *path)
 		h->type = FIFO;
 	}
 
-	memset(h->chksum, ' ', sizeof(h->chksum));
-	for (i = 0, chksum = 0; i < sizeof(*h); i++)
-		chksum += (unsigned char)b[i];
-	putoctal(h->chksum, chksum, sizeof(h->chksum));
+	if (xhdroffset) {
+		xh = (struct header *)xb;
+		memset(xb, 0, sizeof(xb));
+		xh->type = 'x';
+		putoctal(xh->size,    xhdroffset,  sizeof(xh->size));
+		memcpy(  xh->magic,   "ustar",     sizeof(h->magic));
+		memcpy(  xh->version, "00",        sizeof(h->version));
+		fillchksum(xh);
+		ewrite(tarfd, xb, BLKSIZ);
+		ewrite(tarfd, xhdr, xhdroffset);
+		if (xhdroffset % BLKSIZ) {
+			l = BLKSIZ - (xhdroffset % BLKSIZ);
+			memset(xb, 0, l);
+			ewrite(tarfd, xb, l);
+		}
+	}
+
+	fillchksum(h);
 	ewrite(tarfd, b, BLKSIZ);
 
 	if (fd != -1) {
_AT_@ -412,7 +473,7 @@ chktar(struct header *h)
 	const char *reason;
 	long s1, s2, i;
 
-	if (h->prefix[0] == '\0' && h->name[0] == '\0') {
+	if (h->prefix[0] == '\0' && h->name[0] == '\0' && h->type != 'x') {
 		reason = "empty filename";
 		goto bad;
 	}
-- 
2.33.1

Received on Sun May 01 2022 - 14:25:18 CEST