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libphoenx/scanf: Fix SEGFAULT caused by invalid processing of %n #357

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libphoenx/scanf: Fix SEGFAULT caused by invalid processing of %n #357

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astalke
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@astalke astalke commented Apr 22, 2024 •
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Description

  • Fix SEGFAULT caused by invalid processing of %n
  • MISRA

Fixes: phoenix-rtos/phoenix-rtos-project#1059

JIRA: RTOS-825

Motivation and Context

Types of changes

  • Bug fix (non-breaking change which fixes an issue)
  • New feature (non-breaking change which adds functionality)
  • Breaking change (fix or feature that would cause existing functionality to change)

How Has This Been Tested?

  • Already covered by automatic testing.
  • New test added: (add PR link here).
  • Tested by hand on: (list targets here).

Checklist:

  • My change requires a change to the documentation.
  • I have updated the documentation accordingly.
  • I have added tests to cover my changes.
  • All new and existing linter checks and tests passed.
  • My changes generate no new compilation warnings for any of the targets.

Special treatment

  • This PR needs additional PRs to work (list the PRs, preferably in merge-order).
  • I will merge this PR by myself when appropriate.

github-actions[bot]
github-actions bot reviewed Apr 22, 2024
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stdio/scanf.c Outdated Show resolved Hide resolved
@astalke astalke force-pushed the astalke/RTOS-825 branch 2 times, most recently from 1ea9e11 to 364b04b Compare April 22, 2024 10:52
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github-actions bot commented Apr 22, 2024 •
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Unit Test Results

7 460 tests  ±0   6 745 ✅ ±0   39m 10s ⏱️ + 1m 59s
  420 suites ±0     715 💤 ±0 
    1 files   ±0       0 ❌ ±0 

Results for commit c7cf842. ± Comparison against base commit 81b5a09.

♻️ This comment has been updated with latest results.

@astalke astalke marked this pull request as ready for review April 22, 2024 11:40
@agkaminski
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Hmm, tbh I don't get this change. Block handling %n has been moved later in the code, but I can't see any functional change in doing so. Could you please briefly explain this change?

@astalke
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astalke commented Apr 29, 2024

Hmm, tbh I don't get this change. Block handling %n has been moved later in the code, but I can't see any functional change in doing so. Could you please briefly explain this change?

After reviewing my changes, I've noticed that there is an easier fix, so I will upload it soon and let CI check if it really is enough. Bug is caused by a use of continue instead of break, lack of default label in this switch and reusing c variable in the next switch statement. Basically, continue causes loop to execute one too many times, so c == 0, there is no default label to catch that and due to reusing of c in the next switch statement, we execute case CT_CHAR.

@astalke astalke marked this pull request as draft April 30, 2024 10:56
@astalke astalke marked this pull request as ready for review April 30, 2024 10:58
agkaminski
agkaminski previously approved these changes May 15, 2024
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LGTM

Darchiv
Darchiv reviewed May 22, 2024
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stdio/scanf.c
@@ -318,7 +320,10 @@ static int scanf_parse(char *ccltab, const char *inp, int *inr, char const *fmt0
else {
*va_arg(ap, int *) = nread;
}
continue;
break;
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This works because c == 'n' so it won't match any of CT_* values in the conversion switch below. Whitespace will still be skipped anyway. Maybe there should be CT_NONE value which performs no conversion is used for 'n' and default cases, together with NOSKIP?

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@Darchiv Darchiv Awaiting requested review from Darchiv

@agkaminski agkaminski Awaiting requested review from agkaminski

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sscanf produces segfault
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@astalke @agkaminski @Darchiv