From 23c8a812dc3c621009e4f0e5342aa4e2ede1ceaa Mon Sep 17 00:00:00 2001 From: David Howells Date: Tue, 23 Feb 2016 11:03:12 +0000 Subject: [PATCH] KEYS: Fix ASN.1 indefinite length object parsing This fixes CVE-2016-0758. In the ASN.1 decoder, when the length field of an ASN.1 value is extracted, it isn't validated against the remaining amount of data before being added to the cursor. With a sufficiently large size indicated, the check: datalen - dp < 2 may then fail due to integer overflow. Fix this by checking the length indicated against the amount of remaining data in both places a definite length is determined. Whilst we're at it, make the following changes: (1) Check the maximum size of extended length does not exceed the capacity of the variable it's being stored in (len) rather than the type that variable is assumed to be (size_t). (2) Compare the EOC tag to the symbolic constant ASN1_EOC rather than the integer 0. (3) To reduce confusion, move the initialisation of len outside of: for (len = 0; n > 0; n--) { since it doesn't have anything to do with the loop counter n. Signed-off-by: David Howells Reviewed-by: Mimi Zohar Acked-by: David Woodhouse Acked-by: Peter Jones --- lib/asn1_decoder.c | 16 +++++++++------- 1 file changed, 9 insertions(+), 7 deletions(-) diff --git a/lib/asn1_decoder.c b/lib/asn1_decoder.c index 2b3f46c049d45..554522934c442 100644 --- a/lib/asn1_decoder.c +++ b/lib/asn1_decoder.c @@ -74,7 +74,7 @@ static int asn1_find_indefinite_length(const unsigned char *data, size_t datalen /* Extract a tag from the data */ tag = data[dp++]; - if (tag == 0) { + if (tag == ASN1_EOC) { /* It appears to be an EOC. */ if (data[dp++] != 0) goto invalid_eoc; @@ -96,10 +96,8 @@ static int asn1_find_indefinite_length(const unsigned char *data, size_t datalen /* Extract the length */ len = data[dp++]; - if (len <= 0x7f) { - dp += len; - goto next_tag; - } + if (len <= 0x7f) + goto check_length; if (unlikely(len == ASN1_INDEFINITE_LENGTH)) { /* Indefinite length */ @@ -110,14 +108,18 @@ static int asn1_find_indefinite_length(const unsigned char *data, size_t datalen } n = len - 0x80; - if (unlikely(n > sizeof(size_t) - 1)) + if (unlikely(n > sizeof(len) - 1)) goto length_too_long; if (unlikely(n > datalen - dp)) goto data_overrun_error; - for (len = 0; n > 0; n--) { + len = 0; + for (; n > 0; n--) { len <<= 8; len |= data[dp++]; } +check_length: + if (len > datalen - dp) + goto data_overrun_error; dp += len; goto next_tag;