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add reentrant variants of sha1_to_hex and find_unique_abbrev

The sha1_to_hex and find_unique_abbrev functions always
write into reusable static buffers. There are a few problems
with this:

  - future calls overwrite our result. This is especially
    annoying with find_unique_abbrev, which does not have a
    ring of buffers, so you cannot even printf() a result
    that has two abbreviated sha1s.

  - if you want to put the result into another buffer, we
    often strcpy, which looks suspicious when auditing for
    overflows.

This patch introduces sha1_to_hex_r and find_unique_abbrev_r,
which write into a user-provided buffer. Of course this is
just punting on the overflow-auditing, as the buffer
obviously needs to be GIT_SHA1_HEXSZ + 1 bytes. But it is
much easier to audit, since that is a well-known size.

We retain the non-reentrant forms, which just become thin
wrappers around the reentrant ones. This patch also adds a
strbuf variant of find_unique_abbrev, which will be handy in
later patches.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
tags/v2.7.0-rc0
Jeff King Junio C Hamano 4 years ago
parent
commit
af49c6d091
5 changed files with 67 additions and 10 deletions
  1. +30
    -1
      cache.h
  2. +9
    -4
      hex.c
  3. +11
    -5
      sha1_name.c
  4. +9
    -0
      strbuf.c
  5. +8
    -0
      strbuf.h

+ 30
- 1
cache.h View File

@@ -785,7 +785,24 @@ extern char *sha1_pack_name(const unsigned char *sha1);
*/
extern char *sha1_pack_index_name(const unsigned char *sha1);

extern const char *find_unique_abbrev(const unsigned char *sha1, int);
/*
* Return an abbreviated sha1 unique within this repository's object database.
* The result will be at least `len` characters long, and will be NUL
* terminated.
*
* The non-`_r` version returns a static buffer which will be overwritten by
* subsequent calls.
*
* The `_r` variant writes to a buffer supplied by the caller, which must be at
* least `GIT_SHA1_HEXSZ + 1` bytes. The return value is the number of bytes
* written (excluding the NUL terminator).
*
* Note that while this version avoids the static buffer, it is not fully
* reentrant, as it calls into other non-reentrant git code.
*/
extern const char *find_unique_abbrev(const unsigned char *sha1, int len);
extern int find_unique_abbrev_r(char *hex, const unsigned char *sha1, int len);

extern const unsigned char null_sha1[GIT_SHA1_RAWSZ];

static inline int hashcmp(const unsigned char *sha1, const unsigned char *sha2)
@@ -1067,6 +1084,18 @@ extern int for_each_abbrev(const char *prefix, each_abbrev_fn, void *);
extern int get_sha1_hex(const char *hex, unsigned char *sha1);
extern int get_oid_hex(const char *hex, struct object_id *sha1);

/*
* Convert a binary sha1 to its hex equivalent. The `_r` variant is reentrant,
* and writes the NUL-terminated output to the buffer `out`, which must be at
* least `GIT_SHA1_HEXSZ + 1` bytes, and returns a pointer to out for
* convenience.
*
* The non-`_r` variant returns a static buffer, but uses a ring of 4
* buffers, making it safe to make multiple calls for a single statement, like:
*
* printf("%s -> %s", sha1_to_hex(one), sha1_to_hex(two));
*/
extern char *sha1_to_hex_r(char *out, const unsigned char *sha1);
extern char *sha1_to_hex(const unsigned char *sha1); /* static buffer result! */
extern char *oid_to_hex(const struct object_id *oid); /* same static buffer as sha1_to_hex */



+ 9
- 4
hex.c View File

@@ -61,12 +61,10 @@ int get_oid_hex(const char *hex, struct object_id *oid)
return get_sha1_hex(hex, oid->hash);
}

char *sha1_to_hex(const unsigned char *sha1)
char *sha1_to_hex_r(char *buffer, const unsigned char *sha1)
{
static int bufno;
static char hexbuffer[4][GIT_SHA1_HEXSZ + 1];
static const char hex[] = "0123456789abcdef";
char *buffer = hexbuffer[3 & ++bufno], *buf = buffer;
char *buf = buffer;
int i;

for (i = 0; i < GIT_SHA1_RAWSZ; i++) {
@@ -79,6 +77,13 @@ char *sha1_to_hex(const unsigned char *sha1)
return buffer;
}

char *sha1_to_hex(const unsigned char *sha1)
{
static int bufno;
static char hexbuffer[4][GIT_SHA1_HEXSZ + 1];
return sha1_to_hex_r(hexbuffer[3 & ++bufno], sha1);
}

char *oid_to_hex(const struct object_id *oid)
{
return sha1_to_hex(oid->hash);


+ 11
- 5
sha1_name.c View File

@@ -368,14 +368,13 @@ int for_each_abbrev(const char *prefix, each_abbrev_fn fn, void *cb_data)
return ds.ambiguous;
}

const char *find_unique_abbrev(const unsigned char *sha1, int len)
int find_unique_abbrev_r(char *hex, const unsigned char *sha1, int len)
{
int status, exists;
static char hex[41];

memcpy(hex, sha1_to_hex(sha1), 40);
sha1_to_hex_r(hex, sha1);
if (len == 40 || !len)
return hex;
return 40;
exists = has_sha1_file(sha1);
while (len < 40) {
unsigned char sha1_ret[20];
@@ -384,10 +383,17 @@ const char *find_unique_abbrev(const unsigned char *sha1, int len)
? !status
: status == SHORT_NAME_NOT_FOUND) {
hex[len] = 0;
return hex;
return len;
}
len++;
}
return len;
}

const char *find_unique_abbrev(const unsigned char *sha1, int len)
{
static char hex[GIT_SHA1_HEXSZ + 1];
find_unique_abbrev_r(hex, sha1, len);
return hex;
}



+ 9
- 0
strbuf.c View File

@@ -743,3 +743,12 @@ void strbuf_addftime(struct strbuf *sb, const char *fmt, const struct tm *tm)
}
strbuf_setlen(sb, sb->len + len);
}

void strbuf_add_unique_abbrev(struct strbuf *sb, const unsigned char *sha1,
int abbrev_len)
{
int r;
strbuf_grow(sb, GIT_SHA1_HEXSZ + 1);
r = find_unique_abbrev_r(sb->buf + sb->len, sha1, abbrev_len);
strbuf_setlen(sb, sb->len + r);
}

+ 8
- 0
strbuf.h View File

@@ -474,6 +474,14 @@ static inline struct strbuf **strbuf_split(const struct strbuf *sb,
*/
extern void strbuf_list_free(struct strbuf **);

/**
* Add the abbreviation, as generated by find_unique_abbrev, of `sha1` to
* the strbuf `sb`.
*/
extern void strbuf_add_unique_abbrev(struct strbuf *sb,
const unsigned char *sha1,
int abbrev_len);

/**
* Launch the user preferred editor to edit a file and fill the buffer
* with the file's contents upon the user completing their editing. The


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