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: 4f73175d0375 ("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>

diff --git a/lib/oid_registry.c b/lib/oid_registry.c
index 41b9e50711a72af31d7548d3aea5be1177a45a9d..5a75d127995da55f45e814961439b25ba1986b56 100644 (file)
--- a/lib/oid_registry.c
+++ b/lib/oid_registry.c
@@ -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;
        }