From: Chirantan Ekbote chirantan@chromium.org
commit 31070f6ccec09f3bd4f1e28cd1e592fa4f3ba0b6 upstream.
The ioctl encoding for this parameter is a long but the documentation says it should be an int and the kernel drivers expect it to be an int. If the fuse driver treats this as a long it might end up scribbling over the stack of a userspace process that only allocated enough space for an int.
This was previously discussed in [1] and a patch for fuse was proposed in [2]. From what I can tell the patch in [2] was nacked in favor of adding new, "fixed" ioctls and using those from userspace. However there is still no "fixed" version of these ioctls and the fact is that it's sometimes infeasible to change all userspace to use the new one.
Handling the ioctls specially in the fuse driver seems like the most pragmatic way for fuse servers to support them without causing crashes in userspace applications that call them.
[1]: https://lore.kernel.org/linux-fsdevel/20131126200559.GH20559@hall.aurel32.ne... [2]: https://sourceforge.net/p/fuse/mailman/message/31771759/
Signed-off-by: Chirantan Ekbote chirantan@chromium.org Fixes: 59efec7b9039 ("fuse: implement ioctl support") Cc: stable@vger.kernel.org Signed-off-by: Miklos Szeredi mszeredi@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/fuse/file.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-)
--- a/fs/fuse/file.c +++ b/fs/fuse/file.c @@ -18,6 +18,7 @@ #include <linux/swap.h> #include <linux/falloc.h> #include <linux/uio.h> +#include <linux/fs.h>
static struct page **fuse_pages_alloc(unsigned int npages, gfp_t flags, struct fuse_page_desc **desc) @@ -2758,7 +2759,16 @@ long fuse_do_ioctl(struct file *file, un struct iovec *iov = iov_page;
iov->iov_base = (void __user *)arg; - iov->iov_len = _IOC_SIZE(cmd); + + switch (cmd) { + case FS_IOC_GETFLAGS: + case FS_IOC_SETFLAGS: + iov->iov_len = sizeof(int); + break; + default: + iov->iov_len = _IOC_SIZE(cmd); + break; + }
if (_IOC_DIR(cmd) & _IOC_WRITE) { in_iov = iov;