Commit 47e0a208 authored Dec 08, 2017 by Eric Biggers Committed by David Howells Dec 08, 2017

X.509: fix buffer overflow detection in sprint_oid()



In sprint_oid(), if the input buffer were to be more than 1 byte too
small for the first snprintf(), 'bufsize' would underflow, causing a
buffer overflow when printing the remainder of the OID.

Fortunately this cannot actually happen currently, because no users pass
in a buffer that can be too small for the first snprintf().

Regardless, fix it by checking the snprintf() return value correctly.

For consistency also tweak the second snprintf() check to look the same.

Fixes: 4f73175d ("X.509: Add utility functions to render OIDs as strings")
Cc: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: James Morris <james.l.morris@oracle.com>

parent 0f30cbea

lib/oid_registry.c

+4 −4

Original line number	Diff line number	Diff line
		@@ -120,10 +120,10 @@ int sprint_oid(const void data, size_t datasize, char buffer, size_t bufsize)

		n = *v++;
		ret = count = snprintf(buffer, bufsize, "%u.%u", n / 40, n % 40);
		if (count >= bufsize)
		return -ENOBUFS;
		buffer += count;
		bufsize -= count;
		if (bufsize == 0)
		return -ENOBUFS;

		while (v < end) {
		num = 0;
		@@ -141,9 +141,9 @@ int sprint_oid(const void data, size_t datasize, char buffer, size_t bufsize)
		} while (n & 0x80);
		}
		ret += count = snprintf(buffer, bufsize, ".%lu", num);
		buffer += count;
		if (bufsize <= count)
		if (count >= bufsize)
		return -ENOBUFS;
		buffer += count;
		bufsize -= count;
		}

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