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Subject: Although I can't reproduce it, oss-fuzz complains about is_tar
Origin: FILE5_30-19-g7605984c
Upstream-Author: Christos Zoulas <christos@zoulas.com>
Date: Fri Mar 17 20:45:01 2017 +0000
Although I can't reproduce it, oss-fuzz complains about is_tar. So rewrite
it to make it more obvious what's going on.
--- a/src/is_tar.c
+++ b/src/is_tar.c
@@ -51,7 +51,7 @@
#define isodigit(c) ( ((c) >= '0') && ((c) <= '7') )
private int is_tar(const unsigned char *, size_t);
-private int from_oct(int, const char *); /* Decode octal number */
+private int from_oct(const char *, size_t); /* Decode octal number */
static const char tartype[][32] = {
"tar archive",
@@ -93,31 +93,35 @@
is_tar(const unsigned char *buf, size_t nbytes)
{
const union record *header = (const union record *)(const void *)buf;
- int i;
- int sum, recsum;
- const unsigned char *p;
+ size_t i;
+ int sum, recsum;
+ const unsigned char *p, *ep;
- if (nbytes < sizeof(union record))
+ if (nbytes < sizeof(*header))
return 0;
- recsum = from_oct(8, header->header.chksum);
+ recsum = from_oct(header->header.chksum, sizeof(header->header.chksum));
sum = 0;
p = header->charptr;
- for (i = sizeof(union record); --i >= 0;)
+ ep = header->charptr + sizeof(*header);
+ while (p < ep)
sum += *p++;
/* Adjust checksum to count the "chksum" field as blanks. */
- for (i = sizeof(header->header.chksum); --i >= 0;)
+ for (i = 0; i < sizeof(header->header.chksum); i++)
sum -= header->header.chksum[i];
- sum += ' ' * sizeof header->header.chksum;
+ sum += ' ' * sizeof(header->header.chksum);
if (sum != recsum)
return 0; /* Not a tar archive */
- if (strcmp(header->header.magic, GNUTMAGIC) == 0)
+ if (strncmp(header->header.magic, GNUTMAGIC,
+ sizeof(header->header.magic)) == 0)
return 3; /* GNU Unix Standard tar archive */
- if (strcmp(header->header.magic, TMAGIC) == 0)
+
+ if (strncmp(header->header.magic, TMAGIC,
+ sizeof(header->header.magic)) == 0)
return 2; /* Unix Standard tar archive */
return 1; /* Old fashioned tar archive */
@@ -130,19 +134,22 @@
* Result is -1 if the field is invalid (all blank, or non-octal).
*/
private int
-from_oct(int digs, const char *where)
+from_oct(const char *where, size_t digs)
{
int value;
+ if (digs == 0)
+ return -1;
+
while (isspace((unsigned char)*where)) { /* Skip spaces */
where++;
- if (--digs <= 0)
+ if (digs-- == 0)
return -1; /* All blank field */
}
value = 0;
while (digs > 0 && isodigit(*where)) { /* Scan til non-octal */
value = (value << 3) | (*where++ - '0');
- --digs;
+ digs--;
}
if (digs > 0 && *where && !isspace((unsigned char)*where))
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