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x86/vdso: Plug race between mapping and ELF header setup
The vsyscall32 sysctl can racy against a concurrent fork when it switches from disabled to enabled: arch_setup_additional_pages() if (vdso32_enabled) --> No mapping sysctl.vsysscall32() --> vdso32_enabled = true create_elf_tables() ARCH_DLINFO_IA32 if (vdso32_enabled) { --> Add VDSO entry with NULL pointer Make ARCH_DLINFO_IA32 check whether the VDSO mapping has been set up for the newly forked process or not. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Andy Lutomirski <luto@amacapital.net> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Mathias Krause <minipli@googlemail.com> Cc: stable@vger.kernel.org Link: http://lkml.kernel.org/r/20170410151723.602367196@linutronix.de Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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@ -287,7 +287,7 @@ struct task_struct;
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#define ARCH_DLINFO_IA32 \
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do { \
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if (vdso32_enabled) { \
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if (VDSO_CURRENT_BASE) { \
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NEW_AUX_ENT(AT_SYSINFO, VDSO_ENTRY); \
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NEW_AUX_ENT(AT_SYSINFO_EHDR, VDSO_CURRENT_BASE); \
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} \
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