libdpkg: Add tar format detection support

Recognize old tar, GNU tar and ustar formats. Abort on ustar with non
empty Prefix field, as we don't properly handle the long names yet.
Failure for PAX archive is already being handled when acting on the
typeflag.

2 files changed, 23 insertions, 1 deletions

diff --git a/lib/tarfn.c b/lib/tarfn.c
index bdf0bb0c1..ecb5acb21 100644
--- a/lib/tarfn.c
+++ b/lib/tarfn.c
@@ -18,6 +18,9 @@
 #include <dpkg.h>
 #include <dpkg-priv.h>
 
+#define TAR_MAGIC_USTAR "ustar\0" "00"
+#define TAR_MAGIC_GNU   "ustar "  " \0"
+
 struct TarHeader {
 	char Name[100];
 	char Mode[8];
@@ -33,6 +36,7 @@ struct TarHeader {
 	char GroupName[32];
 	char MajorDevice[8];
 	char MinorDevice[8];
+	char Prefix[155];	/* Only valid on ustar. */
 };
 typedef struct TarHeader	TarHeader;
 
@@ -81,12 +85,22 @@ DecodeTarHeader(char * block, TarInfo * d)
 	long			sum;
 	long			checksum;
 
+	if (memcmp(h->MagicNumber, TAR_MAGIC_GNU, 6) == 0)
+		d->format = tar_format_gnu;
+	else if (memcmp(h->MagicNumber, TAR_MAGIC_USTAR, 6) == 0)
+		d->format = tar_format_ustar;
+	else
+		d->format = tar_format_old;
+
 	if ( *h->UserName )
 		passwd = getpwnam(h->UserName);
 	if ( *h->GroupName )
 		group = getgrnam(h->GroupName);
 
-	d->Name = StoC(h->Name, sizeof(h->Name));
+	if (d->format == tar_format_ustar && h->Prefix[0] != '\0')
+		abort();
+	else
+		d->Name = StoC(h->Name, sizeof(h->Name));
 	d->LinkName = StoC(h->LinkName, sizeof(h->LinkName));
 	d->Mode = (mode_t)OtoL(h->Mode, sizeof(h->Mode));
 	d->Size = (size_t)OtoL(h->Size, sizeof(h->Size));
diff --git a/lib/tarfn.h b/lib/tarfn.h
index 4bd0e00f4..469d47699 100644
--- a/lib/tarfn.h
+++ b/lib/tarfn.h
@@ -12,6 +12,13 @@
 #include <unistd.h>
 #include <sys/types.h>
 
+enum tar_format {
+	tar_format_old,
+	tar_format_gnu,
+	tar_format_ustar,
+	tar_format_pax,
+};
+
 enum TarFileType {
 	NormalFile0 = '\0',	/* For compatibility with decades-old bug */
 	NormalFile1 = '0',
@@ -27,6 +34,7 @@ enum TarFileType {
 typedef enum TarFileType	TarFileType;
 
 struct	TarInfo {
+	enum tar_format	format;		/* Tar archive format. */
 	void *		UserData;	/* User passed this in as argument */
 	char *		Name;		/* File name */
 	mode_t		Mode;		/* Unix mode, including device bits. */