mirror of
https://github.com/ukui/kernel.git
synced 2026-03-09 10:07:04 -07:00
Jussi Maki
b2c4618162
The current conversion of skb->data_end reads like this: ; data_end = (void*)(long)skb->data_end; 559: (79) r1 = *(u64 *)(r2 +200) ; r1 = skb->data 560: (61) r11 = *(u32 *)(r2 +112) ; r11 = skb->len 561: (0f) r1 += r11 562: (61) r11 = *(u32 *)(r2 +116) 563: (1f) r1 -= r11 But similar to the case in84f44df664("bpf: sock_ops sk access may stomp registers when dst_reg = src_reg"), the code will read an incorrect skb->len when src == dst. In this case we end up generating this xlated code: ; data_end = (void*)(long)skb->data_end; 559: (79) r1 = *(u64 *)(r1 +200) ; r1 = skb->data 560: (61) r11 = *(u32 *)(r1 +112) ; r11 = (skb->data)->len 561: (0f) r1 += r11 562: (61) r11 = *(u32 *)(r1 +116) 563: (1f) r1 -= r11 ... where line 560 is the reading 4B of (skb->data + 112) instead of the intended skb->len Here the skb pointer in r1 gets set to skb->data and the later deref for skb->len ends up following skb->data instead of skb. This fixes the issue similarly to the patch mentioned above by creating an additional temporary variable and using to store the register when dst_reg = src_reg. We name the variable bpf_temp_reg and place it in the cb context for sk_skb. Then we restore from the temp to ensure nothing is lost. Fixes:16137b09a6("bpf: Compute data_end dynamically with JIT code") Signed-off-by: Jussi Maki <joamaki@gmail.com> Signed-off-by: John Fastabend <john.fastabend@gmail.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Reviewed-by: Jakub Sitnicki <jakub@cloudflare.com> Link: https://lore.kernel.org/bpf/20211103204736.248403-6-john.fastabend@gmail.com
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.