From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=95.215.58.199 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794703897; b=wDeXncC3y/FCVba21tEQ2KjqyX0ngzVxfp84eo7Yjtx0tgEJKOZzg7bG3EHREW7VSvMp vkeTH4mfAC+X3AFjSspkeEEwMG00aDZSaaQeWi9P+DKJzbsV9EWZoBjNWS9ZZMSrs/Krr LRSUjE0tcJHAzhu+mZ88vS5wOSs9caQMDv8FbwTFmBCjFuPXlW3ZTYzhoSX4fUXHPeAaL CB8xy5095/vbdsIu8Bjz3rU06Yk8URyhsqYZN5Ms5h8/oQJxGfIy6zmMWBZ5fFCSEQKi3 Zj/3aXHDy6owy9Dx75qYbK2yrjoJsZXLblrPQgMMELlQ016+dqY/9TgheRnR3/zL9rQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794703897; h=DMARC-Filter:X-Envelope-To:DKIM-Signature:X-Envelope-To:Received: X-Mizu-Trace-ID:X-Migadu-Flow:Date:From:To:CC:Subject:In-Reply-To: Message-ID:MIME-Version:Content-Type:Content-Transfer-Encoding; bh=cIQKJ+UG91RHKyYene2ntrB1MHw8caFD+qmGOAO6wSU=; b=QI5I0KKbx7VMjPHfis9RKBPo8n4p8KDdAbRuAo0Eeu0jMYXUAYA/LLjwRThD2oRS0mh4 rp0Pt0QNDTi31t9R/6jHDl/bvmXTcmHEJ+4V7d0/VxSShYQW9tPWZ4z9ePaV/SIq9R6e5 CD4mktvjwPr8h5N6grSBrd/nK98OVCklSpaaG9LIQ+I0sREiYytYkVQSGjear/FYYM86t TnPy/plyrybWWerYKbf7Z+X9B9EMxfH7gpemRwFNK9PVnePcTVKgNXSDgwwiUomGDXRf4 XhqLZxtzNPOAry14hsKAhbNkYBTKsNWZBjt3ebu6yPf8G1aEt7hsjoj+w6ywZ9ldZ/w== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=SWe59QkV; arc=none smtp.remote-ip=95.215.58.199 Received: from mta1.migadu.com (out-199.mta1.migadu.com [95.215.58.199]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id CA889606A323 for ; Sun, 15 Nov 2026 00:51:35 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org CA889606A323 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=SWe59QkV X-Envelope-To: linux-api@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=xFnLsG59GvlRg1cGX6jqXi1P0i1OqXy1k2drts1zmg0=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1794703893; v=1; x=1795308693; b=SWe59QkVUKTpOuhVSRr4ltJFXxocdeMcga7R0GcwcO0EDL0etq+qIs5/TVyfHi6BVNDn7trL imz1lbQV0oqs9d4PGRQ2flu/5KeG5Ck2h36znDAAhUdCaKbTrlRYVhArXQYR0+6Traj224K3d4W MiSpnRv/orIv1JjypQ1hNdnM= X-Envelope-To: linux-api@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id d6aa2e4d69f7770f; Sun, 15 Nov 2026 00:51:33 +0000 X-Mizu-Trace-ID: d6aa2e4d69f7770f X-Migadu-Flow: FLOW_OUT Date: Sun, 15 Nov 2026 00:51:33 +0000 From: Bradley Morgan To: renzo@cs.unibo.it CC: akpm@linux-foundation.org, evgsyr@gmail.com, ldv@strace.io, legion@kernel.org, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org, oleg@redhat.com, strace-devel@lists.strace.io, thecharlesjenkins@gmail.com Subject: =?US-ASCII?Q?Re=3A_=5BPATCH=5D_ptrace=3A_reject_out_of_range?= =?US-ASCII?Q?_error_values_in_PTRACE=5FSET=5FSYSCALL=5FINFO?= In-Reply-To: <20261114184842.373304-1-renzo@cs.unibo.it> Message-ID: <2D2A202C-35F8-4200-9110-B0E636216FCF@linux.dev> X-Mailing-List: linux-api@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit On 14 November 2026 18:48:40 GMT, Renzo Davoli wrote: >When PTRACE_SET_SYSCALL_INFO is used with op == PTRACE_SYSCALL_INFO_EXIT >and is_error set, info.exit.rval is passed to syscall_set_return_value() >as its "int error" argument. The only check is that rval fits in a >"long", which is a no-op on 64-bit architectures, so: > > - values outside the "int" range are silently truncated; > - a value whose low 32 bits are zero, e.g. 0 or 0x100000000, becomes > error == 0, and the system call returns 0 as a success although the > tracer asked for an error; > - a positive value is stored as is by some architectures (e.g. x86) > and is not seen as an error by the tracee. > >PTRACE_GET_SYSCALL_INFO reports errors as negative errno values, so >reject with -ERANGE any error value outside [-MAX_ERRNO, -1]. > >Fixes: 26bb32768fe6 ("ptrace: introduce PTRACE_SET_SYSCALL_INFO request") >Signed-off-by: Renzo Davoli >Assisted-by: claude-opus-5-5 Drop. No longer needed. Annoyingly. Assisted bys aren't needed no more. :( >--- >This patch is independent of the PTRACE_SET_SYSCALL_INFO syscall skipping >series and applies cleanly either before or after it. > >Tested on x86_64 (QEMU/KVM) with a test program that, at the exit stop of >getpid(), calls PTRACE_SET_SYSCALL_INFO with op == >PTRACE_SYSCALL_INFO_EXIT, >is_error = 1 and the following rval values: > > rval without this patch with this patch > (getpid() in the tracee) > 0 returns 0, success -ERANGE > 1 returns 1, success -ERANGE > ESRCH (3) returns 3, success -ERANGE > -MAX_ERRNO - 1 returns -4096, success -ERANGE > INT_MIN returns INT_MIN, success -ERANGE > 0x100000000 returns 0, success -ERANGE > -0x100000000 - ESRCH fails with ESRCH, but -ERANGE > PTRACE_GET_SYSCALL_INFO > reports rval -3 > -ESRCH fails with ESRCH fails with ESRCH > -MAX_ERRNO fails with errno 4095 fails with errno 4095 > >Without this patch PTRACE_SET_SYSCALL_INFO succeeds in every case, and >on x86_64 syscall_set_return_value() stores the error, truncated to >"int", as is: values outside [-MAX_ERRNO, -1] become successful return >values, so the tracer asks for an error and the tracee sees a success, >or a different error than the one requested. With this patch these >values are rejected and the tracee registers are left untouched; valid >errno values behave as before. That's just word puke. I did NOT read all of that, make it TL;DR preferably. > > kernel/ptrace.c | 8 ++++++++ > 1 file changed, 8 insertions(+) > >diff --git a/kernel/ptrace.c b/kernel/ptrace.c >index 3f2fe68ccb14..2fbd0d55b42e 100644 >--- a/kernel/ptrace.c >+++ b/kernel/ptrace.c >@@ -1111,6 +1111,14 @@ ptrace_set_syscall_info_exit(struct task_struct *child, struct pt_regs *regs, > if (rval != info->exit.rval) > return -ERANGE; > >+ /* >+ * An error is passed to syscall_set_return_value() as an "int" >+ * and must be a negative errno value: anything else would be >+ * truncated or would make the system call succeed. >+ */ This is very verbose. Like VERY verbose. Maybe a one or two liner comment would be way way better >+ if (info->exit.is_error && (rval < -MAX_ERRNO || rval >= 0)) >+ return -ERANGE; >+ > if (info->exit.is_error) > syscall_set_return_value(child, regs, rval, 0); > else > --- Thanks!