[Crash-utility] Re: [PATCH] bugfix command "help -r" segv fault

[lijiang <lijiang@xxxxxxxxxx>]

Hi, Guanyou

Thank you for the fix.

On Mon, Nov 4, 2024 at 4:13 PM <devel-request@xxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:

Date: Fri, 1 Nov 2024 18:01:27 +0800
From: Guanyou Chen <chenguanyou9338@xxxxxxxxx>
Subject: [PATCH] bugfix command "help -r" segv fault
To: Lianbo <lijiang@xxxxxxxxxx>, Tao Liu <ltao@xxxxxxxxxx>,
        devel@xxxxxxxxxxxxxxxxxxxxxxxxxxx
Message-ID:
        <CAHS3RMU3nuiqW4z=Qo9RoufADrUxcaLhyjnxwMCuGODB_+37yQ@xxxxxxxxxxxxxx>
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Hi Lianbo, Tao

When the ELF Note does not contain CPU registers,
attempting to retrieve online CPU registers will cause a crash.

After:
CPU 6:
help: registers not collected for cpu 6
...

Signed-off-by: Guanyou.Chen <chenguanyou@xxxxxxxxxx>
---
 netdump.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/netdump.c b/netdump.c
index 8ea5159..435793b 100644
--- a/netdump.c
+++ b/netdump.c
@@ -2780,6 +2780,10 @@ display_regs_from_elf_notes(int cpu, FILE *ofp)

I copied the code block here:

display_regs_from_elf_notes(int cpu, FILE *ofp)
{
        Elf32_Nhdr *note32;
        Elf64_Nhdr *note64;
        size_t len;
        char *user_regs;
        int c, skipped_count;

        /*
         * Kdump NT_PRSTATUS notes are only related to online cpus,
         * so offline cpus should be skipped.
         */
        if (pc->flags2 & QEMU_MEM_DUMP_ELF)
                skipped_count = 0;
        else {
                for (c = skipped_count = 0; c < cpu; c++) {
                        if (check_offline_cpu(c))
                                skipped_count++;
                }
        }

        if ((cpu - skipped_count) >= nd->num_prstatus_notes &&
             !machine_type("MIPS")) {
                error(INFO, "registers not collected for cpu %d\n", cpu);
                return;
        }

...

Could you please point out why the above check does not work?

BTW: I'm not sure if it can work for you, can you help to try this? Just a guess.

        if (((cpu < 0 ) || (!dd->nt_prstatus_percpu[cpu]) 

             || (cpu - skipped_count) >= nd->num_prstatus_notes) &&
             !machine_type("MIPS")) {

                error(INFO, "registers not collected for cpu %d\n", cpu);
                return;
        }

Thanks

Lianbo

                nd->nt_prstatus_percpu[cpu];
        else
                    note64 = (Elf64_Nhdr *)nd->nt_prstatus;
+       if (!note64) {
+           error(INFO, "registers not collected for cpu %d\n", cpu);
+           return;
+       }
        len = sizeof(Elf64_Nhdr);
        len = roundup(len + note64->n_namesz, 4);
        len = roundup(len + note64->n_descsz, 4);
@@ -2820,6 +2824,10 @@ display_regs_from_elf_notes(int cpu, FILE *ofp)
                nd->nt_prstatus_percpu[cpu];
        else
                    note32 = (Elf32_Nhdr *)nd->nt_prstatus;
+       if (!note32) {
+           error(INFO, "registers not collected for cpu %d\n", cpu);
+           return;
+       }
        len = sizeof(Elf32_Nhdr);
        len = roundup(len + note32->n_namesz, 4);
        len = roundup(len + note32->n_descsz, 4);
@@ -2857,6 +2865,10 @@ display_regs_from_elf_notes(int cpu, FILE *ofp)
        else
            note64 = (Elf64_Nhdr *)nd->nt_prstatus;

+       if (!note64) {
+           error(INFO, "registers not collected for cpu %d\n", cpu);
+           return;
+       }
        prs = (struct ppc64_elf_prstatus *)
            ((char *)note64 + sizeof(Elf64_Nhdr) + note64->n_namesz);
        prs = (struct ppc64_elf_prstatus *)roundup((ulong)prs, 4);
@@ -2903,6 +2915,10 @@ display_regs_from_elf_notes(int cpu, FILE *ofp)
                nd->nt_prstatus_percpu[cpu];
        else
                    note64 = (Elf64_Nhdr *)nd->nt_prstatus;
+       if (!note64) {
+           error(INFO, "registers not collected for cpu %d\n", cpu);
+           return;
+       }
        len = sizeof(Elf64_Nhdr);
        len = roundup(len + note64->n_namesz, 4);
        len = roundup(len + note64->n_descsz, 4);
--
2.34.1

Guanyou.
Thanks

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