On Sat, Mar 21, 2020 at 08:56:20PM -0700, Eric Biggers wrote: > On Wed, Mar 18, 2020 at 09:39:40AM -0700, Eric Biggers wrote: > > On Fri, Mar 13, 2020 at 09:45:11AM -0700, Eric Biggers wrote: > > > On Sat, Mar 07, 2020 at 06:38:49PM -0800, Eric Biggers wrote: > > > > From: Eric Biggers <ebiggers@xxxxxxxxxx> > > > > > > > > Reading from a debugfs file at a nonzero position, without first reading > > > > at position 0, leaks uninitialized memory to userspace. > > > > > > > > It's a bit tricky to do this, since lseek() and pread() aren't allowed > > > > on these files, and write() doesn't update the position on them. But > > > > writing to them with splice() *does* update the position: > > > > > > > > #define _GNU_SOURCE 1 > > > > #include <fcntl.h> > > > > #include <stdio.h> > > > > #include <unistd.h> > > > > int main() > > > > { > > > > int pipes[2], fd, n, i; > > > > char buf[32]; > > > > > > > > pipe(pipes); > > > > write(pipes[1], "0", 1); > > > > fd = open("/sys/kernel/debug/fault_around_bytes", O_RDWR); > > > > splice(pipes[0], NULL, fd, NULL, 1, 0); > > > > n = read(fd, buf, sizeof(buf)); > > > > for (i = 0; i < n; i++) > > > > printf("%02x", buf[i]); > > > > printf("\n"); > > > > } > > > > > > > > Output: > > > > 5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a30 > > > > > > > > Fix the infoleak by making simple_attr_read() always fill > > > > simple_attr::get_buf if it hasn't been filled yet. > > > > > > > > Reported-by: syzbot+fcab69d1ada3e8d6f06b@xxxxxxxxxxxxxxxxxxxxxxxxx > > > > Reported-by: Alexander Potapenko <glider@xxxxxxxxxx> > > > > Fixes: acaefc25d21f ("[PATCH] libfs: add simple attribute files") > > > > Cc: stable@xxxxxxxxxxxxxxx > > > > Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx> > > > > --- > > > > fs/libfs.c | 8 +++++--- > > > > 1 file changed, 5 insertions(+), 3 deletions(-) > > > > > > > > diff --git a/fs/libfs.c b/fs/libfs.c > > > > index c686bd9caac6..3759fbacf522 100644 > > > > --- a/fs/libfs.c > > > > +++ b/fs/libfs.c > > > > @@ -891,7 +891,7 @@ int simple_attr_open(struct inode *inode, struct file *file, > > > > { > > > > struct simple_attr *attr; > > > > > > > > - attr = kmalloc(sizeof(*attr), GFP_KERNEL); > > > > + attr = kzalloc(sizeof(*attr), GFP_KERNEL); > > > > if (!attr) > > > > return -ENOMEM; > > > > > > > > @@ -931,9 +931,11 @@ ssize_t simple_attr_read(struct file *file, char __user *buf, > > > > if (ret) > > > > return ret; > > > > > > > > - if (*ppos) { /* continued read */ > > > > + if (*ppos && attr->get_buf[0]) { > > > > + /* continued read */ > > > > size = strlen(attr->get_buf); > > > > - } else { /* first read */ > > > > + } else { > > > > + /* first read */ > > > > u64 val; > > > > ret = attr->get(attr->data, &val); > > > > if (ret) > > > > -- > > > > 2.25.1 > > > > > > Any comments on this? Al, seems this is something you should pick up? > > > > > > - Eric > > > > Ping. > > > > Andrew, can you consider taking this patch? Al has been ignoring it, and this > seems like a fairly important fix. This bug affects many (most?) debugfs files, > and it affects years old kernels too not just recent ones. As it affects debugfs files, I'll grab it now, thanks. greg k-h