When we test seccomp with 6.4 kernel, we found errno has wrong value.
If we deny NETLINK_AUDIT with EAFNOSUPPORT, after f0bddf50586d, we will
get ENOSYS instead. We got same result with commit 9c2598d43510 ("riscv: entry:
Save a0 prior syscall_enter_from_user_mode()").
After analysing code, we think that regs->a0 = -ENOSYS should only be executed
when syscall != -1 In __seccomp_filter, when seccomp rejected this syscall with
specified errno, they will set a0 to return number as syscall ABI, and then
return -1. This return number is finally pass as return number of
syscall_enter_from_user_mode, and then is compared with NR_syscalls after
converted to ulong (so it will be ULONG_MAX). The condition
syscall < NR_syscalls will always be false, so regs->a0 = -ENOSYS is always
executed. It covered a0 set by seccomp, so we always get ENOSYS when match
seccomp RET_ERRNO rule.
Fixes: f0bddf50586d ("riscv: entry: Convert to generic entry")
Reported-by: Felix Yan <[email protected]>
Co-developed-by: Ruizhe Pan <[email protected]>
Signed-off-by: Ruizhe Pan <[email protected]>
Co-developed-by: Shiqi Zhang <[email protected]>
Signed-off-by: Shiqi Zhang <[email protected]>
Signed-off-by: Celeste Liu <[email protected]>
Tested-by: Felix Yan <[email protected]>
Reviewed-by: Björn Töpel <[email protected]>
Reviewed-by: Guo Ren <[email protected]>
---
v3 -> v4: use long instead of ulong to reduce type cast and avoid
implementation-defined behavior, and make the judgment of syscall
invalid more explicit
v2 -> v3: use if-statement instead of set default value,
clarify the type of syscall
v1 -> v2: added explanation on why always got ENOSYS
arch/riscv/kernel/traps.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
index f910dfccbf5d2..729f79c97e2bf 100644
--- a/arch/riscv/kernel/traps.c
+++ b/arch/riscv/kernel/traps.c
@@ -297,7 +297,7 @@ asmlinkage __visible __trap_section void do_trap_break(struct pt_regs *regs)
asmlinkage __visible __trap_section void do_trap_ecall_u(struct pt_regs *regs)
{
if (user_mode(regs)) {
- ulong syscall = regs->a7;
+ long syscall = regs->a7;
regs->epc += 4;
regs->orig_a0 = regs->a0;
@@ -306,9 +306,9 @@ asmlinkage __visible __trap_section void do_trap_ecall_u(struct pt_regs *regs)
syscall = syscall_enter_from_user_mode(regs, syscall);
- if (syscall < NR_syscalls)
+ if (syscall >= 0 && syscall < NR_syscalls)
syscall_handler(regs, syscall);
- else
+ else if (syscall != -1)
regs->a0 = -ENOSYS;
syscall_exit_to_user_mode(regs);
--
2.41.0
On Thu, 20 Jul 2023 at 16:05, Celeste Liu <[email protected]> wrote:
>
> When we test seccomp with 6.4 kernel, we found errno has wrong value.
> If we deny NETLINK_AUDIT with EAFNOSUPPORT, after f0bddf50586d, we will
> get ENOSYS instead. We got same result with commit 9c2598d43510 ("riscv: entry:
> Save a0 prior syscall_enter_from_user_mode()").
>
> After analysing code, we think that regs->a0 = -ENOSYS should only be executed
> when syscall != -1 In __seccomp_filter, when seccomp rejected this syscall with
> specified errno, they will set a0 to return number as syscall ABI, and then
> return -1. This return number is finally pass as return number of
> syscall_enter_from_user_mode, and then is compared with NR_syscalls after
> converted to ulong (so it will be ULONG_MAX). The condition
> syscall < NR_syscalls will always be false, so regs->a0 = -ENOSYS is always
> executed. It covered a0 set by seccomp, so we always get ENOSYS when match
> seccomp RET_ERRNO rule.
>
> Fixes: f0bddf50586d ("riscv: entry: Convert to generic entry")
> Reported-by: Felix Yan <[email protected]>
> Co-developed-by: Ruizhe Pan <[email protected]>
> Signed-off-by: Ruizhe Pan <[email protected]>
> Co-developed-by: Shiqi Zhang <[email protected]>
> Signed-off-by: Shiqi Zhang <[email protected]>
> Signed-off-by: Celeste Liu <[email protected]>
> Tested-by: Felix Yan <[email protected]>
With this patch I can use groupmod, groupadd, usermod, useradd etc.
inside systemd-nspawn again. Thanks!
Tested-by: Emil Renner Berthing <[email protected]>
> Reviewed-by: Björn Töpel <[email protected]>
> Reviewed-by: Guo Ren <[email protected]>
> ---
>
> v3 -> v4: use long instead of ulong to reduce type cast and avoid
> implementation-defined behavior, and make the judgment of syscall
> invalid more explicit
> v2 -> v3: use if-statement instead of set default value,
> clarify the type of syscall
> v1 -> v2: added explanation on why always got ENOSYS
>
> arch/riscv/kernel/traps.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
> index f910dfccbf5d2..729f79c97e2bf 100644
> --- a/arch/riscv/kernel/traps.c
> +++ b/arch/riscv/kernel/traps.c
> @@ -297,7 +297,7 @@ asmlinkage __visible __trap_section void do_trap_break(struct pt_regs *regs)
> asmlinkage __visible __trap_section void do_trap_ecall_u(struct pt_regs *regs)
> {
> if (user_mode(regs)) {
> - ulong syscall = regs->a7;
> + long syscall = regs->a7;
>
> regs->epc += 4;
> regs->orig_a0 = regs->a0;
> @@ -306,9 +306,9 @@ asmlinkage __visible __trap_section void do_trap_ecall_u(struct pt_regs *regs)
>
> syscall = syscall_enter_from_user_mode(regs, syscall);
>
> - if (syscall < NR_syscalls)
> + if (syscall >= 0 && syscall < NR_syscalls)
> syscall_handler(regs, syscall);
> - else
> + else if (syscall != -1)
> regs->a0 = -ENOSYS;
>
> syscall_exit_to_user_mode(regs);
> --
> 2.41.0
>
>
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