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get_sha1_hex(): do not read past a NUL character

Previously, get_sha1_hex() would read one character past the end of a
null-terminated string whose strlen was an even number less than 40.
Although the function correctly returned -1 in these cases, the extra
memory access might have been to uninitialized (or even, conceivably,
unallocated) memory.

Add a check to avoid reading past the end of a string.

This problem was discovered by Thomas Rast <trast@student.ethz.ch>
using valgrind.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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commit d4e85a1afe0a3310a3c8336c2824775901cc27d7 1 parent 3793ac5
Michael Haggerty mhagger authored gitster committed
Showing with 18 additions and 1 deletion.
  1. +9 −0 cache.h
  2. +9 −1 hex.c
9 cache.h
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@@ -819,7 +819,16 @@ static inline int get_sha1_with_context(const char *str, unsigned char *sha1, st
{
return get_sha1_with_context_1(str, sha1, orc, 0, NULL);
}
+
+/*
+ * Try to read a SHA1 in hexadecimal format from the 40 characters
+ * starting at hex. Write the 20-byte result to sha1 in binary form.
+ * Return 0 on success. Reading stops if a NUL is encountered in the
+ * input, so it is safe to pass this function an arbitrary
+ * null-terminated string.
+ */
extern int get_sha1_hex(const char *hex, unsigned char *sha1);
+
extern char *sha1_to_hex(const unsigned char *sha1); /* static buffer result! */
extern int read_ref(const char *filename, unsigned char *sha1);
extern const char *resolve_ref(const char *path, unsigned char *sha1, int, int *);
10 hex.c
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@@ -39,7 +39,15 @@ int get_sha1_hex(const char *hex, unsigned char *sha1)
{
int i;
for (i = 0; i < 20; i++) {
- unsigned int val = (hexval(hex[0]) << 4) | hexval(hex[1]);
+ unsigned int val;
+ /*
+ * hex[1]=='\0' is caught when val is checked below,
+ * but if hex[0] is NUL we have to avoid reading
+ * past the end of the string:
+ */
+ if (!hex[0])
+ return -1;
+ val = (hexval(hex[0]) << 4) | hexval(hex[1]);
if (val & ~0xff)
return -1;
*sha1++ = val;
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