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author | Eric Biggers <ebiggers@google.com> | 2020-03-07 18:38:49 -0800 |
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committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2020-03-24 13:27:16 +0100 |
commit | a65cab7d7f05c2061a3e2490257d3086ff3202c6 (patch) | |
tree | 897fff31b7feb585234c26ed50745dbc5cba7e69 /fs/libfs.c | |
parent | 4dbe191c046e71d6ea1ba85365ecb33961b07c4f (diff) | |
download | linux-a65cab7d7f05c2061a3e2490257d3086ff3202c6.tar.gz |
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("\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@syzkaller.appspotmail.com Reported-by: Alexander Potapenko <glider@google.com> Fixes: acaefc25d21f ("[PATCH] libfs: add simple attribute files") Cc: stable@vger.kernel.org Signed-off-by: Eric Biggers <ebiggers@google.com> Acked-by: Kees Cook <keescook@chromium.org> Link: https://lore.kernel.org/r/20200308023849.988264-1-ebiggers@kernel.org Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'fs/libfs.c')
-rw-r--r-- | fs/libfs.c | 8 |
1 files 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) |