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Use explicit_bzero() if available by michaelortmann · Pull Request #148 · swaywm/swaylock · GitHub
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Use explicit_bzero() if available - #148

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michaelortmann:explicit_bzero
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Use explicit_bzero() if available#148
michaelortmann wants to merge 4 commits into
swaywm:masterfrom
michaelortmann:explicit_bzero

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@michaelortmann

@michaelortmann michaelortmann commented Jul 16, 2020

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Use explicit_bzero() if available

The 'volatile' solution may not work as expected

Quote from https://www.gnu.org/software/libc/manual/html_node/Erasing-Sensitive-Data.html:

Declaring sensitive variables as volatile will make both the above problems worse; a volatile variable will be stored in memory for its entire lifetime, and the compiler will make more copies of it than it would otherwise have. Attempting to erase a normal variable “by hand” through a volatile-qualified pointer doesn’t work at all—because the variable itself is not volatile, some compilers will ignore the qualification on the pointer and remove the erasure anyway.

emersion
emersion reviewed Jul 21, 2020
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@emersion

emersion commented Jul 21, 2020

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The 'volatile' solution may not work as expected

This isn't much of an issue: volatile isn't used for the sensitive data, instead it's used for the zeroes.

@emersion

emersion commented Aug 10, 2020

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Yeah, this requires _GNU_SOURCE as I thought.

I'm not sure it's worth it to maintain this extra complexity for unclear benefits.

@emersion

emersion commented Aug 14, 2021

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Sorry, I'm going to close this, we prefer to avoid non-POSIX functions.

@emersion emersion closed this Aug 14, 2021
@nmeum

nmeum commented Mar 30, 2024 •
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Sorry, I'm going to close this, we prefer to avoid non-POSIX functions.

You cannot reliably zero memory without avoiding non-POSIX functions. explicit_bzero is nowadays implemented by OpenBSD, musl libc, and glibc (i.e. it is widely available). If you rely on the volatile keyword, chances are that the zero'ing is optimized out by the compiler. For more background information refer to https://media.ccc.de/v/35c3-9788-memsad

@nmeum nmeum mentioned this pull request Mar 30, 2024
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nmeum commented Mar 30, 2024

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Since this issue has been closed for a couple of years now, I have opened #353 with a somewhat simpler implementation in the hopes of resuming the discussion there.

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