From f956575ffd112277366c0cb91ed30e118a0b49fb Mon Sep 17 00:00:00 2001 From: Ritesh Harjani Date: Mon, 19 Mar 2018 16:03:09 +0530 Subject: [PATCH] ANDROID: fuse: Add null terminator to path in canonical path to avoid issue page allocated in fuse_dentry_canonical_path to be handled in fuse_dev_do_write is allocated using __get_free_pages(GFP_KERNEL). This may not return a page with data filled with 0. Now this page may not have a null terminator at all. If this happens and userspace fuse daemon screws up by passing a string to kernel which is not NULL terminated (or did not fill anything), then inside fuse driver in kernel when we try to do strlen(fuse_dev_write->kern_path->getname_kernel) on that page data -> it may give us issue with kernel paging request. Unable to handle kernel paging request at virtual address ------------[ cut here ]------------ <..> PC is at strlen+0x10/0x90 LR is at getname_kernel+0x2c/0xf4 <..> strlen+0x10/0x90 kern_path+0x28/0x4c fuse_dev_do_write+0x5b8/0x694 fuse_dev_write+0x74/0x94 do_iter_readv_writev+0x80/0xb8 do_readv_writev+0xec/0x1cc vfs_writev+0x54/0x64 SyS_writev+0x64/0xe4 el0_svc_naked+0x24/0x28 To avoid this we should ensure in case of FUSE_CANONICAL_PATH, the page is null terminated. Change-Id: I33ca7cc76b4472eaa982c67bb20685df451121f5 Signed-off-by: Ritesh Harjani Bug: 75984715 [Daniel - small edit, using args size ] Signed-off-by: Daniel Rosenberg --- fs/fuse/dev.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c index 032485010a05..968b79823502 100644 --- a/fs/fuse/dev.c +++ b/fs/fuse/dev.c @@ -1892,8 +1892,10 @@ static ssize_t fuse_dev_do_write(struct fuse_dev *fud, err = copy_out_args(cs, &req->out, nbytes); if (req->in.h.opcode == FUSE_CANONICAL_PATH) { - req->out.h.error = kern_path((char *)req->out.args[0].value, 0, - req->canonical_path); + char *path = (char *)req->out.args[0].value; + + path[req->out.args[0].size - 1] = 0; + req->out.h.error = kern_path(path, 0, req->canonical_path); } fuse_copy_finish(cs); -- 2.20.1