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SubjectRe: KASAN: slab-out-of-bounds Read in bpf_prog_create
Arnd and Al,

On Tue, Sep 17, 2019 at 11:49:06AM -0700, syzbot wrote:
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit: 2015a28f Add linux-next specific files for 20190915
> git tree: linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=11880d69600000
> kernel config: https://syzkaller.appspot.com/x/.config?x=110691c2286b679a
> dashboard link: https://syzkaller.appspot.com/bug?extid=eb853b51b10f1befa0b7
> compiler: gcc (GCC) 9.0.0 20181231 (experimental)
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=127c3481600000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1150a70d600000
>
> The bug was bisected to:
>
> commit 2f4fa2db75e26995709043c8d3de4632ebed5c4b
> Author: Al Viro <viro@zeniv.linux.org.uk>
> Date: Thu Apr 18 03:48:01 2019 +0000
>
> compat_ioctl: unify copy-in of ppp filters
>
> bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=145eee1d600000
> final crash: https://syzkaller.appspot.com/x/report.txt?x=165eee1d600000
> console output: https://syzkaller.appspot.com/x/log.txt?x=125eee1d600000
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+eb853b51b10f1befa0b7@syzkaller.appspotmail.com
> Fixes: 2f4fa2db75e2 ("compat_ioctl: unify copy-in of ppp filters")
>
> ==================================================================
> BUG: KASAN: slab-out-of-bounds in memcpy include/linux/string.h:404 [inline]
> BUG: KASAN: slab-out-of-bounds in bpf_prog_create+0xe9/0x250
> net/core/filter.c:1351
> Read of size 32768 at addr ffff88809cf74000 by task syz-executor183/8575
>
> CPU: 0 PID: 8575 Comm: syz-executor183 Not tainted 5.3.0-rc8-next-20190915
> #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> Call Trace:
> __dump_stack lib/dump_stack.c:77 [inline]
> dump_stack+0x172/0x1f0 lib/dump_stack.c:113
> print_address_description.constprop.0.cold+0xd4/0x30b mm/kasan/report.c:374
> __kasan_report.cold+0x1b/0x41 mm/kasan/report.c:506
> kasan_report+0x12/0x20 mm/kasan/common.c:634
> check_memory_region_inline mm/kasan/generic.c:185 [inline]
> check_memory_region+0x134/0x1a0 mm/kasan/generic.c:192
> memcpy+0x24/0x50 mm/kasan/common.c:122
> memcpy include/linux/string.h:404 [inline]
> bpf_prog_create+0xe9/0x250 net/core/filter.c:1351
> get_filter.isra.0+0x108/0x1a0 drivers/net/ppp/ppp_generic.c:572
> ppp_get_filter drivers/net/ppp/ppp_generic.c:584 [inline]
> ppp_ioctl+0x129d/0x2590 drivers/net/ppp/ppp_generic.c:801

This is a correct bisection. This commit needs:

diff --git a/drivers/net/ppp/ppp_generic.c b/drivers/net/ppp/ppp_generic.c
index 267fe2c58087..f55d7937d6c5 100644
--- a/drivers/net/ppp/ppp_generic.c
+++ b/drivers/net/ppp/ppp_generic.c
@@ -564,8 +564,9 @@ static struct bpf_prog *get_filter(struct sock_fprog *uprog)
return NULL;

/* uprog->len is unsigned short, so no overflow here */
- fprog.len = uprog->len * sizeof(struct sock_filter);
- fprog.filter = memdup_user(uprog->filter, fprog.len);
+ fprog.len = uprog->len;
+ fprog.filter = memdup_user(uprog->filter,
+ uprog->len * sizeof(struct sock_filter));
if (IS_ERR(fprog.filter))
return ERR_CAST(fprog.filter);

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