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libdraw: fix out of bounds memory access after subfont array reallocation (thanks ray)

Browse source 
/n/bugs/open/libdrawfont.c_buffer_overflow
http://bugs.9front.org/open/libdrawfont.c_buffer_overflow/readme

ray@raylai.com

Hi all,

In plan9port this bug keeps crashing mc when I run lc in a directory with Chinese characters. This is a diff from OpenBSD but it should apply cleanly to the various plan9 sources.

The code is basically trying to do a realloc (I guess realloc wasn't available back then?) but it copies too much from the original buffer.

Since realloc is available, just use it. If realloc isn't available outside plan9port (I haven't checked) the memmove line should be changed from:
	memmove(f->subf, of, (f->nsubf+DSUBF)*sizeof *subf);
to:
	memmove(f->subf, of, f->nsubf*sizeof *subf);

I hope this is helpful.

Ray
This commit is contained in:
cinap_lenrek 2016-04-05 11:24:07 +02:00
parent a74542613d
commit 796e7b84bd
1 changed files with 2 additions and 4 deletions
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6
sys/src/libdraw/font.c
View file

@ -216,16 +216,14 @@ loadchar(Font *f, Rune r, Cacheinfo *c, int h, int noflush, char **subfontname)
subf->age = 0;
}else{ /* too recent; grow instead */
of = f->subf;
f->subf = malloc((f->nsubf+DSUBF)*sizeof *subf);
f->subf = realloc(of, (f->nsubf+DSUBF)*sizeof *subf);
if(f->subf == nil){
f->subf = of;
goto Toss;
}
memmove(f->subf, of, (f->nsubf+DSUBF)*sizeof *subf);
memset(f->subf+f->nsubf, 0, DSUBF*sizeof *subf);
subf = &f->subf[f->nsubf];
memset(subf, 0, DSUBF*sizeof *subf);
f->nsubf += DSUBF;
free(of);
}
}
subf->age = 0;