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542fbda0f0
The dst entry might already have a zero refcount, waiting on rcu list
to be free'd. Using dst_hold() transitions its reference count to 1, and
next dst release will try to free it again -- resulting in a double free:
WARNING: CPU: 1 PID: 0 at include/net/dst.h:239 nf_xfrm_me_harder+0xe7/0x130 [nf_nat]
RIP: 0010:nf_xfrm_me_harder+0xe7/0x130 [nf_nat]
Code: 48 8b 5c 24 60 65 48 33 1c 25 28 00 00 00 75 53 48 83 c4 68 5b 5d 41 5c c3 85 c0 74 0d 8d 48 01 f0 0f b1 0a 74 86 85 c0 75 f3 <0f> 0b e9 7b ff ff ff 29 c6 31 d2 b9 20 00 48 00 4c 89 e7 e8 31 27
Call Trace:
nf_nat_ipv4_out+0x78/0x90 [nf_nat_ipv4]
nf_hook_slow+0x36/0xd0
ip_output+0x9f/0xd0
ip_forward+0x328/0x440
ip_rcv+0x8a/0xb0
Use dst_hold_safe instead and bail out if we cannot take a reference.
Fixes: a4c2fd7f78 ("net: remove DST_NOCACHE flag")
Reported-by: Martin Zaharinov <micron10@gmail.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
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.