8ab49526b5
syzbot found its way in 86_fsgsbase_read_task() and triggered this oops: KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f] CPU: 0 PID: 6866 Comm: syz-executor262 Not tainted 5.8.0-syzkaller #0 RIP: 0010:x86_fsgsbase_read_task+0x16d/0x310 arch/x86/kernel/process_64.c:393 Call Trace: putreg32+0x3ab/0x530 arch/x86/kernel/ptrace.c:876 genregs32_set arch/x86/kernel/ptrace.c:1026 [inline] genregs32_set+0xa4/0x100 arch/x86/kernel/ptrace.c:1006 copy_regset_from_user include/linux/regset.h:326 [inline] ia32_arch_ptrace arch/x86/kernel/ptrace.c:1061 [inline] compat_arch_ptrace+0x36c/0xd90 arch/x86/kernel/ptrace.c:1198 __do_compat_sys_ptrace kernel/ptrace.c:1420 [inline] __se_compat_sys_ptrace kernel/ptrace.c:1389 [inline] __ia32_compat_sys_ptrace+0x220/0x2f0 kernel/ptrace.c:1389 do_syscall_32_irqs_on arch/x86/entry/common.c:84 [inline] __do_fast_syscall_32+0x57/0x80 arch/x86/entry/common.c:126 do_fast_syscall_32+0x2f/0x70 arch/x86/entry/common.c:149 entry_SYSENTER_compat_after_hwframe+0x4d/0x5c This can happen if ptrace() or sigreturn() pokes an LDT selector into FS or GS for a task with no LDT and something tries to read the base before a return to usermode notices the bad selector and fixes it. The fix is to make sure ldt pointer is not NULL. Fixes: 07e1d88adaae ("x86/fsgsbase/64: Fix ptrace() to read the FS/GS base accurately") Co-developed-by: Jann Horn <jannh@google.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Reported-by: syzbot <syzkaller@googlegroups.com> Acked-by: Andy Lutomirski <luto@kernel.org> Cc: Chang S. Bae <chang.seok.bae@intel.com> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Markus T Metzger <markus.t.metzger@intel.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ravi Shankar <ravi.v.shankar@intel.com> Cc: Rik van Riel <riel@surriel.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@kernel.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.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.