Wednesday, August 5

baron-samedit

daily challenge8

today's brief

January 2021. Qualys researchers reveal Baron Samedit, a bug that sat in sudo for almost ten years and let any local user become root. The heart of it was sudo mishandling backslash escapes while measuring a command line: it got the decoded length wrong and overran a buffer. Here is that measurement, done safely. A backslash escapes the next character, so an escape pair counts as one, and a lone backslash at the very end must not send you reading past the string.

Repair this code

Repair the length count so each backslash escape folds into a single character.

Steps

Count the decoded length of s. A plain character counts as one.
A backslash escapes the next character: the pair counts as a single character, so skip the escaped character when counting.
A lone backslash at the very end has nothing to escape: count it as one character, and do not read past the terminator.
The starter counts every raw byte and ignores escapes. Fix it to fold each escape pair into one character.

examples

$ decoded_len("abc")

$ decoded_len("x\\ny")

$ decoded_len("a\\")

Constraints

Expected files

unescape.c

Allowed functions

None. Write every helper yourself.

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Solutions

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