Undefined behaviour in mprintf#5722
Closed
stoeckmann wants to merge 2 commits into
Closed
Conversation
Verify that specified parameters are in range. If parameters are too large, fail early on and avoid out of boundary accesses. Also do not read behind boundaries of illegal format strings. These are defensive measures since it is expected that format strings are well-formed. Format strings should not be modifiable by user input due to possible generic format string attacks.
Member
|
Thanks, but this seems to make test 557 fail sometimes. example |
Member
|
BTW, it would be awesome if we could also add test cases that reproduce these problems and then these fixes. Can you see if you can add that to lib557.c ? |
Contributor
Author
|
I have added a test case for this. |
Stack overflows can occur with precisions for integers and floats.
Proof of concepts:
- curl_mprintf("%d, %.*1$d", 500, 1);
- curl_mprintf("%d, %+0500.*1$f", 500, 1);
Ideally, compile with -fsanitize=address which makes this undefined
behavior a bit more defined for debug purposes.
The format strings are valid. The overflows occur due to invalid
arguments. If these arguments are variables with contents controlled
by an attacker, the function's stack can be corrupted.
Also see CVE-2016-9586 which partially fixed the float aspect.
Signed-off-by: Tobias Stoeckmann <tobias@stoeckmann.org>
bagder
approved these changes
Jul 26, 2020
jay
pushed a commit
that referenced
this pull request
Jul 27, 2020
Stack overflows can occur with precisions for integers and floats.
Proof of concepts:
- curl_mprintf("%d, %.*1$d", 500, 1);
- curl_mprintf("%d, %+0500.*1$f", 500, 1);
Ideally, compile with -fsanitize=address which makes this undefined
behavior a bit more defined for debug purposes.
The format strings are valid. The overflows occur due to invalid
arguments. If these arguments are variables with contents controlled
by an attacker, the function's stack can be corrupted.
Also see CVE-2016-9586 which partially fixed the float aspect.
Signed-off-by: Tobias Stoeckmann <tobias@stoeckmann.org>
Closes #5722
Member
|
Thanks |
This file contains hidden or 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
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
3 participants
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.
Refactoring of mprintf code to prevent undefined behaviour (signed integer overflows and out of boundary accesses).