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[92.242.249.94]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-4606f2b0d70sm46775690f8f.19.2026.06.16.10.41.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 16 Jun 2026 10:41:22 -0700 (PDT) From: Jakov Novak To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , Sasha Levin , linux-kernel-mentees@lists.linux.dev, Shuah Khan , Alexei Starovoitov , Hsin-Wei Hung , Florian Lehner , Jakov Novak Subject: [PATCH 5.15.y] mm: Fix copy_from_user_nofault(). Date: Tue, 16 Jun 2026 19:40:10 +0200 Message-ID: <20260616174009.9906-2-jakovnovak30@gmail.com> X-Mailer: git-send-email 2.54.0 Precedence: bulk X-Mailing-List: linux-kernel-mentees@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Alexei Starovoitov [ Upstream commit d319f344561de23e810515d109c7278919bff7b0 ] There are several issues with copy_from_user_nofault(): - access_ok() is designed for user context only and for that reason it has WARN_ON_IN_IRQ() which triggers when bpf, kprobe, eprobe and perf on ppc are calling it from irq. - it's missing nmi_uaccess_okay() which is a nop on all architectures except x86 where it's required. The comment in arch/x86/mm/tlb.c explains the details why it's necessary. Calling copy_from_user_nofault() from bpf, [ke]probe without this check is not safe. - __copy_from_user_inatomic() under CONFIG_HARDENED_USERCOPY is calling check_object_size()->__check_object_size()->check_heap_object()->find_vmap_area()->spin_lock() which is not safe to do from bpf, [ke]probe and perf due to potential deadlock. Fix all three issues. At the end the copy_from_user_nofault() becomes equivalent to copy_from_user_nmi() from safety point of view with a difference in the return value. Reported-by: Hsin-Wei Hung Signed-off-by: Alexei Starovoitov Signed-off-by: Florian Lehner Tested-by: Hsin-Wei Hung Tested-by: Florian Lehner Link: https://lore.kernel.org/r/20230410174345.4376-2-dev@der-flo.net [ merge conflicts copy_from_user_nofault: caused by force_uaccess_begin and force_uaccess_end functions. moved the code around to call those functions in the same way after the additional checks. check_heap_object: completely different implementation in 5.15.y. removed any changes from this commit as the current implementation doesn't call the same lock which caused problems. ] Signed-off-by: Jakov Novak --- Note: I have checked all syzbot issues linked with this backport and verified that they work locally (the ones with repros) and on the syzbot servers and I ran KUnit tests to make sure this doesn't break anything. This is my first time sending a patch to the stable repo, so I am a bit unsure if there is more to be done for testing, apart from inspecting the code and running those mentioned tests. mm/maccess.c | 18 ++++++++++++------ 1 file changed, 12 insertions(+), 6 deletions(-) diff --git a/mm/maccess.c b/mm/maccess.c index ded4bfaba7f3..2b186ce822c9 100644 --- a/mm/maccess.c +++ b/mm/maccess.c @@ -5,6 +5,7 @@ #include #include #include +#include bool __weak copy_from_kernel_nofault_allowed(const void *unsafe_src, size_t size) @@ -221,13 +222,18 @@ long strncpy_from_kernel_nofault(char *dst, const void *unsafe_addr, long count) long copy_from_user_nofault(void *dst, const void __user *src, size_t size) { long ret = -EFAULT; - mm_segment_t old_fs = force_uaccess_begin(); + mm_segment_t old_fs; - if (access_ok(src, size)) { - pagefault_disable(); - ret = __copy_from_user_inatomic(dst, src, size); - pagefault_enable(); - } + if (!__access_ok(src, size)) + return ret; + + if (!nmi_uaccess_okay()) + return ret; + + old_fs = force_uaccess_begin(); + pagefault_disable(); + ret = __copy_from_user_inatomic(dst, src, size); + pagefault_enable(); force_uaccess_end(old_fs); if (ret) -- 2.54.0