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Fix and document BIO_FLAGS_NONCLEAR_RST behavior on memory BIO

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The BIO_FLAGS_NONCLEAR_RST flag behavior was not properly documented
and it also caused the length to be incorrectly set after the reset
operation.

Reviewed-by: Bernd Edlinger <bernd.edlinger@hotmail.de>
Reviewed-by: Paul Dale <paul.dale@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/9179)
This commit is contained in:
Tomas Mraz 2019-06-18 16:41:48 +02:00
parent a1998897f6
commit 8b7b32921e
3 changed files with 59 additions and 11 deletions
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4
crypto/bio/bss_mem.c
View file

@ -259,9 +259,7 @@ static long mem_ctrl(BIO *b, int cmd, long num, void *ptr)
bm = bbm->buf;
if (bm->data != NULL) {
if (!(b->flags & BIO_FLAGS_MEM_RDONLY)) {
if (b->flags & BIO_FLAGS_NONCLEAR_RST) {
bm->length = bm->max;
} else {
if (!(b->flags & BIO_FLAGS_NONCLEAR_RST)) {
memset(bm->data, 0, bm->max);
bm->length = 0;
}

26
doc/man3/BIO_s_mem.pod
View file

@ -41,9 +41,10 @@ If the BIO_CLOSE flag is set when a memory BIO is freed then the underlying
BUF_MEM structure is also freed.
Calling BIO_reset() on a read write memory BIO clears any data in it if the
flag BIO_FLAGS_NONCLEAR_RST is not set. On a read only BIO or if the flag
BIO_FLAGS_NONCLEAR_RST is set it restores the BIO to its original state and
the data can be read again.
flag BIO_FLAGS_NONCLEAR_RST is not set, otherwise it just restores the read
pointer to the state it was just after the last write was performed and the
data can be read again. On a read only BIO it similarly restores the BIO to
its original state and the read only data can be read again.
BIO_eof() is true if no data is in the BIO.
@ -79,11 +80,11 @@ first, so the supplied area of memory must be unchanged until the BIO is freed.
Writes to memory BIOs will always succeed if memory is available: that is
their size can grow indefinitely.
Every read from a read write memory BIO will remove the data just read with
an internal copy operation, if a BIO contains a lot of data and it is
read in small chunks the operation can be very slow. The use of a read only
memory BIO avoids this problem. If the BIO must be read write then adding
a buffering BIO to the chain will speed up the process.
Every write after partial read (not all data in the memory buffer was read)
to a read write memory BIO will have to move the unread data with an internal
copy operation, if a BIO contains a lot of data and it is read in small
chunks intertwined with writes the operation can be very slow. Adding
a buffering BIO to the chain can speed up the process.
Calling BIO_set_mem_buf() on a BIO created with BIO_new_secmem() will
give undefined results, including perhaps a program crash.
@ -104,6 +105,15 @@ BIO is set to BIO_NOCLOSE, before freeing the BUF_MEM the data pointer
in it must be set to NULL as the data pointer does not point to an
allocated memory.
Calling BIO_reset() on a read write memory BIO with BIO_FLAGS_NONCLEAR_RST
flag set can have unexpected outcome when the reads and writes to the
BIO are intertwined. As documented above the BIO will be reset to the
state after the last completed write operation. The effects of reads
preceeding that write operation cannot be undone.
Calling BIO_get_mem_ptr() prior to a BIO_reset() call with
BIO_FLAGS_NONCLEAR_RST set has the same effect as a write operation.
=head1 BUGS
There should be an option to set the maximum size of a memory BIO.

40
test/bio_memleak_test.c
View file

@ -181,6 +181,45 @@ finish:
return ok;
}
static int test_bio_nonclear_rst(void)
{
int ok = 0;
BIO *bio = NULL;
char data[16];
bio = BIO_new(BIO_s_mem());
if (!TEST_ptr(bio))
goto finish;
if (!TEST_int_eq(BIO_puts(bio, "Hello World\n"), 12))
goto finish;
BIO_set_flags(bio, BIO_FLAGS_NONCLEAR_RST);
if (!TEST_int_eq(BIO_read(bio, data, 16), 12))
goto finish;
if (!TEST_mem_eq(data, 12, "Hello World\n", 12))
goto finish;
if (!TEST_int_gt(BIO_reset(bio), 0))
goto finish;
if (!TEST_int_eq(BIO_read(bio, data, 16), 12))
goto finish;
if (!TEST_mem_eq(data, 12, "Hello World\n", 12))
goto finish;
BIO_clear_flags(bio, BIO_FLAGS_NONCLEAR_RST);
if (!TEST_int_gt(BIO_reset(bio), 0))
goto finish;
if (!TEST_int_lt(BIO_read(bio, data, 16), 1))
goto finish;
ok = 1;
finish:
BIO_free(bio);
return ok;
}
int global_init(void)
{
@ -196,5 +235,6 @@ int setup_tests(void)
ADD_TEST(test_bio_new_mem_buf);
ADD_TEST(test_bio_rdonly_mem_buf);
ADD_TEST(test_bio_rdwr_rdonly);
ADD_TEST(test_bio_nonclear_rst);
return 1;
}