When realloc(3) fails, it returns NULL and keeps the original allocation
intact. REFTABLE_ALLOC_GROW overwrites both the original pointer and
the allocation count variable in that case, simultaneously leaking the
original allocation and misrepresenting the number of storable items.
parse_names() avoids the leak by keeping the original pointer if
reallocation fails, but still increase the allocation count in such a
case as if it succeeded. That's OK, because the error handling code
just frees everything and doesn't look at names_cap anymore.
reftable_buf_add() does the same, but here it is a problem as it leaves
the reftable_buf in a broken state, with ->alloc being roughly twice as
big as the actually allocated memory, allowing out-of-bounds writes in
subsequent calls.
Reimplement REFTABLE_ALLOC_GROW to avoid leaks, keep allocation counts
in sync and still signal failures to callers while avoiding code
duplication in callers. Make it an expression that evaluates to 0 if no
reallocation is needed or it succeeded and 1 on failure while keeping
the original pointer and allocation counter values.
Adjust REFTABLE_ALLOC_GROW_OR_NULL to the new calling convention for
REFTABLE_ALLOC_GROW, but keep its support for non-size_t alloc variables
for now.
Signed-off-by: René Scharfe <l.s.r@xxxxxx>
---
reftable/basics.c | 11 +++------
reftable/basics.h | 39 +++++++++++++++++++++-----------
t/unit-tests/t-reftable-basics.c | 26 +++++++++++++++++++++
3 files changed, 55 insertions(+), 21 deletions(-)
diff --git a/reftable/basics.c b/reftable/basics.c
index 70b1091d14..cd6b39dbe9 100644
--- a/reftable/basics.c
+++ b/reftable/basics.c
@@ -124,11 +124,8 @@ int reftable_buf_add(struct reftable_buf *buf, const void *data, size_t len)
size_t newlen = buf->len + len;
if (newlen + 1 > buf->alloc) {
- char *reallocated = buf->buf;
- REFTABLE_ALLOC_GROW(reallocated, newlen + 1, buf->alloc);
- if (!reallocated)
+ if (REFTABLE_ALLOC_GROW(buf->buf, newlen + 1, buf->alloc))
return REFTABLE_OUT_OF_MEMORY_ERROR;
- buf->buf = reallocated;
}
memcpy(buf->buf + buf->len, data, len);
@@ -233,11 +230,9 @@ char **parse_names(char *buf, int size)
next = end;
}
if (p < next) {
- char **names_grown = names;
- REFTABLE_ALLOC_GROW(names_grown, names_len + 1, names_cap);
- if (!names_grown)
+ if (REFTABLE_ALLOC_GROW(names, names_len + 1,
+ names_cap))
goto err;
- names = names_grown;
names[names_len] = reftable_strdup(p);
if (!names[names_len++])
diff --git a/reftable/basics.h b/reftable/basics.h
index 259f4c274c..4bf71b0954 100644
--- a/reftable/basics.h
+++ b/reftable/basics.h
@@ -120,22 +120,35 @@ char *reftable_strdup(const char *str);
#define REFTABLE_ALLOC_ARRAY(x, alloc) (x) = reftable_malloc(st_mult(sizeof(*(x)), (alloc)))
#define REFTABLE_CALLOC_ARRAY(x, alloc) (x) = reftable_calloc((alloc), sizeof(*(x)))
#define REFTABLE_REALLOC_ARRAY(x, alloc) (x) = reftable_realloc((x), st_mult(sizeof(*(x)), (alloc)))
-#define REFTABLE_ALLOC_GROW(x, nr, alloc) \
- do { \
- if ((nr) > alloc) { \
- alloc = 2 * (alloc) + 1; \
- if (alloc < (nr)) \
- alloc = (nr); \
- REFTABLE_REALLOC_ARRAY(x, alloc); \
- } \
- } while (0)
+
+static inline void *reftable_alloc_grow(void *p, size_t nelem, size_t elsize,
+ size_t *allocp)
+{
+ void *new_p;
+ size_t alloc = *allocp * 2 + 1;
+ if (alloc < nelem)
+ alloc = nelem;
+ new_p = reftable_realloc(p, st_mult(elsize, alloc));
+ if (!new_p)
+ return p;
+ *allocp = alloc;
+ return new_p;
+}
+
+#define REFTABLE_ALLOC_GROW(x, nr, alloc) ( \
+ (nr) > (alloc) && ( \
+ (x) = reftable_alloc_grow((x), (nr), sizeof(*(x)), &(alloc)), \
+ (nr) > (alloc) \
+ ) \
+)
#define REFTABLE_ALLOC_GROW_OR_NULL(x, nr, alloc) do { \
- void *reftable_alloc_grow_or_null_orig_ptr = (x); \
- REFTABLE_ALLOC_GROW((x), (nr), (alloc)); \
- if (!(x)) { \
- reftable_free(reftable_alloc_grow_or_null_orig_ptr); \
+ size_t reftable_alloc_grow_or_null_alloc = alloc; \
+ if (REFTABLE_ALLOC_GROW((x), (nr), reftable_alloc_grow_or_null_alloc)) { \
+ REFTABLE_FREE_AND_NULL(x); \
alloc = 0; \
+ } else { \
+ alloc = reftable_alloc_grow_or_null_alloc; \
} \
} while (0)
diff --git a/t/unit-tests/t-reftable-basics.c b/t/unit-tests/t-reftable-basics.c
index 5bf79c9976..990dc1a244 100644
--- a/t/unit-tests/t-reftable-basics.c
+++ b/t/unit-tests/t-reftable-basics.c
@@ -146,6 +146,32 @@ int cmd_main(int argc UNUSED, const char *argv[] UNUSED)
check_int(in, ==, out);
}
+ if_test ("REFTABLE_ALLOC_GROW works") {
+ int *arr = NULL, *old_arr;
+ size_t alloc = 0, old_alloc;
+
+ check(!REFTABLE_ALLOC_GROW(arr, 1, alloc));
+ check(arr != NULL);
+ check_uint(alloc, >=, 1);
+ arr[0] = 42;
+
+ old_alloc = alloc;
+ old_arr = arr;
+ reftable_set_alloc(malloc, realloc_stub, free);
+ check(REFTABLE_ALLOC_GROW(arr, old_alloc + 1, alloc));
+ check(arr == old_arr);
+ check_uint(alloc, ==, old_alloc);
+
+ old_alloc = alloc;
+ reftable_set_alloc(malloc, realloc, free);
+ check(!REFTABLE_ALLOC_GROW(arr, old_alloc + 1, alloc));
+ check(arr != NULL);
+ check_uint(alloc, >, old_alloc);
+ arr[alloc - 1] = 42;
+
+ reftable_free(arr);
+ }
+
if_test ("REFTABLE_ALLOC_GROW_OR_NULL works") {
int *arr = NULL;
size_t alloc = 0, old_alloc;
--
2.47.1
