[hackers] [sbase] tar: Explain reason for malformed header || Michael Forney

From: <git_AT_suckless.org>
Date: Tue, 22 Aug 2017 13:40:39 +0200 (CEST)

commit 772a40188bf1c8a2612ac13967bad94228c561a4
Author: Michael Forney <mforney_AT_mforney.org>
AuthorDate: Fri Feb 3 14:56:49 2017 -0800
Commit: Hiltjo Posthuma <hiltjo_AT_codemadness.org>
CommitDate: Tue Aug 22 13:35:29 2017 +0200

    tar: Explain reason for malformed header

diff --git a/tar.c b/tar.c
index f213039..53a737c 100644
--- a/tar.c
+++ b/tar.c
_AT_@ -404,30 +404,38 @@ sanitize(struct header *h)
 static void
 chktar(struct header *h)
 {
- char tmp[8], *err;
- char *p = (char *)h;
+ char tmp[8], *err, *p = (char *)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') {
+ reason = "empty filename";
                 goto bad;
- if (h->magic[0] && strncmp("ustar", h->magic, 5))
+ }
+ if (h->magic[0] && strncmp("ustar", h->magic, 5)) {
+ reason = "not ustar format";
                 goto bad;
+ }
         memcpy(tmp, h->chksum, sizeof(tmp));
         for (i = 0; i < sizeof(tmp); i++)
                 if (tmp[i] == ' ')
                         tmp[i] = '\0';
         s1 = strtol(tmp, &err, 8);
- if (s1 < 0 || *err != '\0')
+ if (s1 < 0 || *err != '\0') {
+ reason = "invalid checksum";
                 goto bad;
+ }
         memset(h->chksum, ' ', sizeof(h->chksum));
         for (i = 0, s2 = 0; i < sizeof(*h); i++)
                 s2 += (unsigned char)p[i];
- if (s1 != s2)
+ if (s1 != s2) {
+ reason = "incorrect checksum";
                 goto bad;
+ }
         memcpy(h->chksum, tmp, sizeof(h->chksum));
         return;
 bad:
- eprintf("malformed tar archive\n");
+ eprintf("malformed tar archive: %s\n", reason);
 }
 
 static void
Received on Tue Aug 22 2017 - 13:40:39 CEST