From 84179e3ce4008f36cbdbb4edf040d94b5f03b4c2 Mon Sep 17 00:00:00 2001 From: Joel Brobecker Date: Thu, 6 Aug 2015 22:13:32 +0200 Subject: [PATCH] [DTRACE] ignore invalid DOF provider sections On x86-solaris 10, we noticed that starting a program would sometimes cause the debugger to crash. For instance: % gdb a (gdb) break adainit Breakpoint 1 at 0x8051f03 (gdb) run Starting program: /[...]/a [Thread debugging using libthread_db enabled] zsh: 24398 segmentation fault (core dumped) /[...]/gdb a The exception occurs in dtrace_process_dof_probe, while trying to process each probe referenced by a DTRACE_DOF_SECT_TYPE_PROVIDER DOF section from /lib/libc.so.1. For reference, the ELF section in that shared library providing the DOF data has the following characteristics: Idx Name Size VMA LMA File off Algn 14 .SUNW_dof 0000109d 000b4398 000b4398 000b4398 2**3 CONTENTS, ALLOC, LOAD, READONLY, DATA The function dtrace_process_dof gets passed the contents of that ELF section, which allows is to determine the location of the table where all DOF sections are described. I dumped the contents of each DOF section as seen by GDB, and it seemed to be plausible, because the offset of each DOF section was pretty much equal to the sum of the offset and size of the previous DOF section. Also, the offset + sum of the last section corresponds to the size of the .SUNW_dof section. Things start to break down when processing one of the DOF sections that has a type of DTRACE_DOF_SECT_TYPE_PROVIDER. It gets the contents of this DOF section via: struct dtrace_dof_provider *provider = (struct dtrace_dof_provider *) DTRACE_DOF_PTR (dof, DOF_UINT (dof, section->dofs_offset)); Said more simply, the struct dtrace_dof_provider data is at section->dofs_offset of the entire DOF contents. Given that the contents of SECTION seemed to make sense, so far so good. However, what SECTION tells us is that our DOF provider section is 40 bytes long: (gdb) print *section $36 = {dofs_type = 15, dofs_align = 4, dofs_flags = 1, dofs_entsize = 0, dofs_offset = 3264, dofs_size = 40} ^^^^^^^^^^^^^^ But on the other hand: (gdb) p sizeof (struct dtrace_dof_provider) $54 = 44 In other words GDB expected a bigger DOF section and when we try to fetch the value of the last field of that DOF section (dofpv_prenoffs)... eoffsets_s = DTRACE_DOF_SECT (dof, DOF_UINT (dof, provider->dofpv_prenoffs)); ... we end up reading data that actually belongs to another DOF section, and therefore irrelevant. This in turn means that the value of eofftab gets incorrectly set, since it depends on eoffsets_s: eofftab = DTRACE_DOF_PTR (dof, DOF_UINT (dof, eoffsets_s->dofs_offset)); This invalid address quickly catches up to us when we pass it to dtrace_process_dof_probe shortly after, where we crash because we try to subscript it: Program received signal SIGSEGV, Segmentation fault. 0x08155bba in dtrace_process_dof_probe ([...]) at [...]/dtrace-probe.c:378 378 = ((uint32_t *) eofftab)[...]; This patch fixes the issue by detecting provider DOF sections that are smaller than expected, and discarding the DOF data. gdb/ChangeLog: * dtrace-probe.c (dtrace_process_dof): Ignore the objfile's DOF data if a DTRACE_DOF_SECT_TYPE_PROVIDER section is found to be smaller than expected. --- gdb/dtrace-probe.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/gdb/dtrace-probe.c b/gdb/dtrace-probe.c index 3f2548d..9816f07 100644 --- a/gdb/dtrace-probe.c +++ b/gdb/dtrace-probe.c @@ -519,6 +519,14 @@ dtrace_process_dof (asection *sect, struct objfile *objfile, unsigned int entsize = DOF_UINT (dof, probes_s->dofs_entsize); int num_probes; + if (DOF_UINT (dof, section->dofs_size) + < sizeof (struct dtrace_dof_provider)) + { + /* The section is smaller than expected, so do not use it. + This has been observed on x86-solaris 10. */ + goto invalid_dof_data; + } + /* Very, unlikely, but could crash gdb if not handled properly. */ if (entsize == 0) -- 1.7.10.4