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b=Dz7cmopBXbpWZFEY5lwdPnHhoDBxWatG6S77ihR9vfdasn+oWaloQ8R8lz3gxY6dT +vthFNb1napSOAVqSuIxn3UbERXOCSzoM+dTow0p9FsDrVfmyK2ZAOysq1DvqrjTuO a3RnFSddTRDoNXb87FctjFGMt+vp9N79ImfLBw+TPyagm1eTt01fJ/95GWGbGODkmP lDGfD+3TY6IAX2dv8jnmmQZFrxVfZ0ChPR0+nkWLPosBSsk2/8u5Yb+j3YsP2AxEM4 vB0UUl6PXrh7qZRI9STSEd1It7kIqdW1Mjn1kH52b39balPfjAubcqi6O+ZCahGoF4 /acHfYNM/IzGg== From: SeongJae Park To: Stanislav Fort Cc: SeongJae Park , damon@lists.linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Stanislav Fort , Andrew Morton Subject: Re: [PATCH v2] mm/damon/sysfs: fix use-after-free in state_show() Date: Fri, 5 Sep 2025 13:12:50 -0700 Message-Id: <20250905201250.36561-1-sj@kernel.org> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20250905101046.2288-1-disclosure@aisle.com> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: C6D31120007 X-Stat-Signature: oswex3yi3dpg3wk5ze4nmkh8cjb6p6qe X-Rspam-User: X-Rspamd-Server: rspam06 X-HE-Tag: 1757103173-42415 X-HE-Meta: U2FsdGVkX1+XsxYaQHyDaj+lf1IGoXSm/Zd+LnC6If04cuQfK7ttNSanEmxeLJLZ6dykOpK4zYbDcviTY3CV7FQ7rNjUC/aofWuBc5LUpS7qakDUtseGaMBwNXg2j+tWi/PYWyaM3qYCJUHd1h5UMZDqjzkBV50qkpnmAgRo1cZ3p5bGLRlzVgp1nlNG7DnpRx9ydaLVhCeBcBuA0WJqlNvQFPhfcas7jUqmBohJanJSbyYBlSiMLn5PFoWpVXQYP/svcy2FTGXRmkHoqlWICn6ZuN/eHlFDZerPcM1QTjSN2EiQm/FjNC3iz/M2UdSytXsUKtpaiD1UjfddoV00qdGaA1Q56hgZVCw2HVGHlWcMgc0Oz6LFlumfsAMnNyKRTNaJjjZXjydItdyeqNVaoYBOE23tO6+eQrIpyw+oEVCbD9JjT9ZQLq2jQpF0fIbPY4mYRc6IobdT1MbDRg95kVFSX7IBUTkhryGAqUBh6CLkf+2jtjmiUlQ3DpERbIKLJFu30uSNWV9G5zQ7zp7MGEeXdk2901v2J4/RfGyMnIST0GfsV5gwd4S8LpzxLGFRoFEOfa2cZgUxsIJRPJcqmp88a28IhlhZ5r2X5qvbrE1Cy2aZW9H9z9VO4+JG7yb1leVgWcQUtU3PR13I2vmFHHH00sn4yfXGpT/qHikFIhbm4vbufEyRQ+dGbCW361sO9FWCloBhlajU0ENG1gCeDZP29zgtpA/FQMc7GfQwXZEy7j6yytuFzorYkj3V0hL5UHvr5fw9B6gkRpvao0sQPDo1zO+cVw2YEX1spJGnzN0u2h2Miu3VejAz96rHzjKEHQfb8v8v0mgx24+l/EXpAYy4x/+tMgpB4thrcY77N7xtMz+GFoeD/dmg5P2xEyjbzd9spBTG2cix8R9t9TJq9OVfx6ygUWQaa+h3SQaK9Q8QFHrkYVat8kzK9Q/UzMA2 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: + Andrew On Fri, 5 Sep 2025 13:10:46 +0300 Stanislav Fort wrote: > state_show() reads kdamond->damon_ctx without holding damon_sysfs_lock. > This allows a use-after-free race: > > CPU 0 CPU 1 > ----- ----- > state_show() damon_sysfs_turn_damon_on() > ctx = kdamond->damon_ctx; mutex_lock(&damon_sysfs_lock); > damon_destroy_ctx(kdamond->damon_ctx); > kdamond->damon_ctx = NULL; > mutex_unlock(&damon_sysfs_lock); > damon_is_running(ctx); /* ctx is freed */ > mutex_lock(&ctx->kdamond_lock); /* UAF */ > > (The race can also occur with damon_sysfs_kdamonds_rm_dirs() and > damon_sysfs_kdamond_release(), which free or replace the context under > damon_sysfs_lock.) > > Fix by taking damon_sysfs_lock before dereferencing the context, > mirroring the locking used in pid_show(). > > The bug has existed since state_show() first accessed kdamond->damon_ctx. > > Fixes: a61ea561c871 ("mm/damon/sysfs: link DAMON for virtual address spaces monitoring") > Reported-by: Stanislav Fort > Closes: N/A # non-publicly reported > Signed-off-by: Stanislav Fort Reviewed-by: SeongJae Park Thanks, SJ [...]