Guard from undefined behaviour in case of an INT_MAX max_pathlen #3192
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
AndrzejKurek
added
enhancement
mbed TLS team
needs-review
|
Attaching a dump of certificates with the changed
|
Patater
suggested changes
Apr 14, 2020
library/x509_crt.c
Outdated
| @@ -524,6 +524,11 @@ static int x509_get_basic_constraints( unsigned char **p, | |||
| return( MBEDTLS_ERR_X509_INVALID_EXTENSIONS + | |||
| MBEDTLS_ERR_ASN1_LENGTH_MISMATCH ); | |||
|
|
|||
| // Do not accept max_pathlen equal to INT_MAX due to size constraints | |||
There was a problem hiding this comment.
Style: Use C-style comments; add a period at the end of sentences
library/x509_crt.c
Outdated
| @@ -524,6 +524,11 @@ static int x509_get_basic_constraints( unsigned char **p, | |||
| return( MBEDTLS_ERR_X509_INVALID_EXTENSIONS + | |||
| MBEDTLS_ERR_ASN1_LENGTH_MISMATCH ); | |||
|
|
|||
| // Do not accept max_pathlen equal to INT_MAX due to size constraints | |||
There was a problem hiding this comment.
What are the size constraints? Isn't this to avoid undefined behaviour when we would do signed integer overflow on line 532 below?
There was a problem hiding this comment.
Yes it is, maybe calling this a size constraint isn't precise enough? :)
There was a problem hiding this comment.
If the comment said what your commit message said: "to avoid signed integer overflow, which is undefined behavior" that'd be good enough
| Zdn977+Sn5anAFGHDWeKo8GYaYGnPBQqkX0Q2EKWR7yrwcKMogOevxELogB0jRj3 | ||
| L+nBpz7mO2J6XQ85ip+tLWAGCEHo0omAIQorAoCSqtLiaz47HxOdNK0hnM7V5k8P | ||
| 05AVhxDa3WqZ9FmMaDc8j8XqmOgKYVMC4/WS0g== | ||
| -----END CERTIFICATE----- |
| mGrpywSV7RpZC2PznGFdqQehwwnOscz0cVeMQqGcMRH3D5Bk2SjVexCaPu47QSyE | ||
| fNm6cATiNHjw/2dg5Aue7e4K+R6le+xY3Qy85Fq/lKDeMmbrJRrNyJ9lblCeihUd | ||
| qhkAEPelpaq5ZRM6cYJQoo0Ak64j4svjOZeF0g== | ||
| -----END CERTIFICATE----- |
Patater
reviewed
Apr 14, 2020
| @@ -1798,6 +1798,14 @@ X509 CRT ASN1 (TBS, inv extBasicConstraint, no pathlen length) | |||
| depends_on:MBEDTLS_RSA_C:MBEDTLS_SHA256_C | |||
| x509parse_crt:"3081b030819aa0030201028204deadbeef300d06092a864886f70d01010b0500300c310a30080600130454657374301c170c303930313031303030303030170c303931323331323335393539300c310a30080600130454657374302a300d06092A864886F70D010101050003190030160210ffffffffffffffffffffffffffffffff0202ffffa100a200a314301230100603551d130101010406300402010102300d06092a864886f70d01010b0500030200ff":"":MBEDTLS_ERR_X509_INVALID_EXTENSIONS + MBEDTLS_ERR_ASN1_OUT_OF_DATA | |||
|
|
|||
| X509 CRT ASN1 (inv extBasicConstraint, pathlen is INT_MAX) | |||
| depends_on:MBEDTLS_RSA_C:MBEDTLS_SHA256_C | |||
There was a problem hiding this comment.
CI says you didn't depend on MBEDTLS_SHA1_C, but should
AndrzejKurek
force-pushed
the
max_pathlen_overflow
branch
from
3f43101 to
ce50d9d
Compare
When parsing a certificate with the basic constraints extension the max_pathlen that was read from it was incremented regardless of its value. However, if the max_pathlen is equal to INT_MAX (which is highly unlikely), an undefined behaviour would occur. This commit adds a check to ensure that such value is not accepted as valid. Relevant tests for INT_MAX and INT_MAX-1 are also introduced. Certificates added in this commit were generated using the test_suite_x509write, function test_x509_crt_check. Input data taken from the "Certificate write check Server1 SHA1" test case, so the generated files are like the "server1.crt", but with the "is_ca" field set to 1 and max_pathlen as described by the file name. Signed-off-by: Andrzej Kurek <andrzej.kurek@arm.com>
AndrzejKurek
force-pushed
the
max_pathlen_overflow
branch
from
ce50d9d to
1605074
Compare
|
Only MbedOS fails on the CI. |
|
Only Mbed OS CI is failing, which is a known issue unrelated to this PR and being worked on. Good to go. |
Patater
removed
needs-ci
This was referenced Apr 17, 2020
gilles-peskine-arm
added a commit
to gilles-peskine-arm/mbedtls
that referenced
this pull request
Apr 21, 2020
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
gilles-peskine-arm
added a commit
to gilles-peskine-arm/mbedtls
that referenced
this pull request
Apr 21, 2020
…low fix Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
gilles-peskine-arm
added a commit
to gilles-peskine-arm/mbedtls
that referenced
this pull request
Apr 28, 2020
…low fix Backport of Mbed-TLS#3192 Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
gilles-peskine-arm
added a commit
to gilles-peskine-arm/mbedtls
that referenced
this pull request
Apr 28, 2020
…low fix Backport of Mbed-TLS#3192 Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
When parsing a certificate with the basic constraints extension, the
max_pathlenthat was read from it was incremented regardless of its value. However, if themax_pathlenis equal toINT_MAX(which is highly unlikely), an undefined behaviour would occur. This commit adds a check to ensure that such value is not accepted as valid. Relevant tests forINT_MAXandINT_MAX-1are also introduced.Certificates added in this commit were generated using the
test_suite_x509write, functiontest_x509_crt_check. Input data taken from the "Certificate write check Server1 SHA1" test case, so the generated files are like the "server1.crt", but with the "is_ca" field set to 1 and max_pathlen as described by the file name.This PR addresses IOTSSL-2774.