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block-crypto: Fix off-by-one in keypath #396

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block-crypto: Fix off-by-one in keypath #396

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4 changes: 2 additions & 2 deletions drivers/block-crypto.c
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Original file line number Diff line number Diff line change
Expand Up @@ -143,8 +143,8 @@ find_keyfile(char **keyfile, const char *dirs,
safe_strncpy(keydir, dirs, sizeof(keydir));
dirs = NULL;
} else {
size_t len = sep - dirs;
safe_strncpy(keydir, dirs, len);
size_t len = (sep - dirs) + 1;
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This may fix the newly introduced bug but the code is still buggy because nothing guarantees that len < sizeof(keydir). I think something like this should work:

size_t len = sep - dirs;
strncpy(keydir, dirs, MIN(len, sizeof(keydir) - 1));
...

This should result in no more than 255 characters copied and the 256th char is guaranteed to be NUL since keydir is zero-initialized.

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@crogers1 crogers1 Feb 13, 2024 •
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I can change it to add that guarantee. Also just to clarify, I assume you want to keep the call to safe_strncpy instead of going back to the old strncpy?

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@crogers1 tbh given that this code is exclusively within an #ifdef OPEN_XT we really couldn't care less about whether you use strncpy or safe_strncpy as we don't even compile this code.

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Understood. I'd still like to keep it consistent with the rest of blktap so I'll leave the safe_strncpy in. Appreciate y'all giving this a review.

safe_strncpy(keydir, dirs, MIN(len, sizeof(keydir)));
dirs = sep+1;
}

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