From 878b30c0bc1446ba933dc4539438512766183500 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?G=C3=BCnther=20Noack?= Date: Mon, 17 Aug 2020 21:11:56 +0200 Subject: [PATCH] fspread: fix buffer overflow Without this fix, fspread is trusting the server to return as much data as requested, or less. If a server responds with more data though, fspread writes beyond the bounds of the buffer to fill, which is passed in by the caller. It depends on the caller of fspread() where that buffer is, so there are various possible attack vectors. In the Plan9 kernel, I found this implemented in devmnt.c, where overly large responses are truncated to the size requested before copying, so I assume that this strategy works here too. This also affects fsread() and fsreadn(), which are based on fspread(). --- src/lib9pclient/read.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-) diff --git a/src/lib9pclient/read.c b/src/lib9pclient/read.c index ea94e9aa..aaf84326 100644 --- a/src/lib9pclient/read.c +++ b/src/lib9pclient/read.c @@ -13,6 +13,7 @@ fspread(CFid *fid, void *buf, long n, vlong offset) Fcall tx, rx; void *freep; uint msize; + long nr; msize = fid->fs->msize - IOHDRSZ; if(n > msize) @@ -34,17 +35,21 @@ fspread(CFid *fid, void *buf, long n, vlong offset) free(freep); return -1; } - if(rx.count){ - memmove(buf, rx.data, rx.count); + nr = rx.count; + if(nr > n) + nr = n; + + if(nr){ + memmove(buf, rx.data, nr); if(offset == -1){ qlock(&fid->lk); - fid->offset += rx.count; + fid->offset += nr; qunlock(&fid->lk); } } free(freep); - return rx.count; + return nr; } long