@@ -891,7 +891,7 @@ int simple_attr_open(struct inode *inode
{
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 *fi
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)
The patch titled Subject: libfs: fix infoleak in simple_attr_read() has been added to the -mm tree. Its filename is libfs-fix-infoleak-in-simple_attr_read.patch This patch should soon appear at http://ozlabs.org/~akpm/mmots/broken-out/libfs-fix-infoleak-in-simple_attr_read.patch and later at http://ozlabs.org/~akpm/mmotm/broken-out/libfs-fix-infoleak-in-simple_attr_read.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ From: Eric Biggers <ebiggers@google.com> Subject: libfs: fix infoleak in simple_attr_read() 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(" "); } Output: 5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a30 Fix the infoleak by making simple_attr_read() always fill simple_attr::get_buf if it hasn't been filled yet. Link: http://lkml.kernel.org/r/20200308023849.988264-1-ebiggers@kernel.org Fixes: acaefc25d21f ("[PATCH] libfs: add simple attribute files") Signed-off-by: Eric Biggers <ebiggers@google.com> Reported-by: syzbot+fcab69d1ada3e8d6f06b@syzkaller.appspotmail.com Reported-by: Alexander Potapenko <glider@google.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: "Rafael J. Wysocki" <rafael@kernel.org> Cc: Kees Cook <keescook@chromium.org> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> --- fs/libfs.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-)