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Re: ncurses buffer overflows (fwd)

From: Jouko Pynnönen
Subject: Re: ncurses buffer overflows (fwd)
Date: Mon, 2 Oct 2000 20:33:19 +0300 (EEST)

On Mon, 2 Oct 2000, Thomas E. Dickey wrote:

> ...and does it break if we limit the strcpy's in lib_mvcur.c ?

My sense says yes, but I haven't tried yet.

> (it's a small change to relatively stable code: it would make more sense
> to distribute the patch than rely on someone else to deduce it).

Hmm, there are many strcpy's in that file, one in repeated_append (doesn't
seem so dangerous, at least tries to check bounds), a few in relative_move
(dangerous), a few in onscreen_mvcur (dangerous).

Fix alternatives IMHO:
1) As far as I can see, it would be safe to change them all to 
strncpy(a,b,OPT_SIZE-1) and do null-termination. They all seem to have
char use[OPT_SIZE] as the destination.

2) The loading routines could (should?) limit the entry length, that would
fix using things like /dev/zero to consume resources. It's not enough
alone though. Even a short terminfo entry having things like %09999d could
still overflow the buffer.

3) tparm() could limit the length of the returned string to OPT_SIZE-1, so
its result could never overflow a buffer (except it the application is
stupid enough to strcpy() them to a smaller buffer, or similar).

4) The terminfo loaded could skip TERMINFO_PATHS and $HOME/.terminfo/ if
the program runs setuid/setgid. How many people need a "customized"
terminfo anyway? Almost none, and how many setuid/setgid programs need
ncurses? Almost none. This would also fix possible unrevealed problems in
parsing a terminfo file or other library functions...

One more thing: in parse_format() or something like that, there are two
variables for the %123.456d type field length and precision. They're
declared int; if someone uses length that's greater than 0x7fffffff and a
small precision value, space will be allocated for the small number of
bytes, because (int)0x7fffffff < small number. And sprintf() will overflow
the buffer if libc parses the number as unsigned int.


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