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d=suse.de; s=susede2_ed25519; t=1750862617; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=FD72zej979ENYi/ObT0PetOUDVERiJGiuNohzLPb6e0=; b=760L25EzwU1ZJigzfRL+HXy4Qd/wX3Diu9GTuiAet4Qmyxj2YWWuBMV5rQdLpz05Nck20M vteKgCV0kZy9b0DQ== Received: from imap1.dmz-prg2.suse.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by imap1.dmz-prg2.suse.org (Postfix) with ESMTPS id 5662713485; Wed, 25 Jun 2025 14:43:37 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id dQ2eExkLXGjwGgAAD6G6ig (envelope-from ); Wed, 25 Jun 2025 14:43:37 +0000 Message-ID: Date: Wed, 25 Jun 2025 16:43:25 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCHv3] gdb: linux-namespaces: enter user namespace when appropriate To: Andrew Burgess , gdb-patches@sourceware.org Cc: Benjamin Berg References: <824ee908821f07452286730643c1efd5f8b01eb2.1749741769.git.aburgess@redhat.com> <87qzzak1ct.fsf@redhat.com> <68c9f369-bd11-48dd-90c8-8c7a61771de7@suse.de> <87ecv8jejc.fsf@redhat.com> <9656c79d-fb13-4689-9254-d59262d9ca6c@suse.de> <878qlfkivv.fsf@redhat.com> Content-Language: en-US From: Tom de Vries In-Reply-To: <878qlfkivv.fsf@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Spamd-Result: default: False [-4.30 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; TO_MATCH_ENVRCPT_ALL(0.00)[]; MIME_TRACE(0.00)[0:+]; ARC_NA(0.00)[]; FUZZY_BLOCKED(0.00)[rspamd.com]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_HAS_DN(0.00)[]; RCPT_COUNT_THREE(0.00)[3]; TO_DN_SOME(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; RCVD_TLS_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; RCVD_VIA_SMTP_AUTH(0.00)[]; MID_RHS_MATCH_FROM(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo] X-BeenThere: gdb-patches@sourceware.org X-Mailman-Version: 2.1.30 Precedence: list List-Id: Gdb-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: gdb-patches-bounces~public-inbox=simark.ca@sourceware.org On 6/25/25 16:15, Andrew Burgess wrote: > Tom de Vries writes: > >> On 6/25/25 12:34, Andrew Burgess wrote: >>> Tom de Vries writes: >>> >>>> On 6/23/25 15:56, Andrew Burgess wrote: >>>>> Andrew Burgess writes: >>>>> >>>>>> From: Benjamin Berg >>>>>> >>>>>> In v2: >>>>>> >>>>>> - Update the test to ignore a warning seen when running the test on >>>>>> a machine with libc debug information installed, but without the >>>>>> libc source being available, e.g.: >>>>>> >>>>>> warning: 46 ../sysdeps/unix/sysv/linux/arm/libc-do-syscall.S: No such file or directory >>>>>> >>>>>> This was causing some CI failures to be reported from Linaro. >>>>>> >>>>>> - Rebased to current upstream/master. >>>>>> >>>>>> In v3: >>>>>> >>>>>> - Same as V2, but fix the test pattern correctly this time. >>>>>> >>>>>> -- >>>>>> >>>>>> The use of user namespaces is required for normal users to use mount >>>>>> namespaces. Consider trying this as an unprivileged user: >>>>>> >>>>>> $ unshare --mount /bin/true >>>>>> unshare: unshare failed: Operation not permitted >>>>>> >>>>>> The problem here is that an unprivileged user doesn't have the >>>>>> required permissions to create a new mount namespace. If, instead, we >>>>>> do this: >>>>>> >>>>>> $ unshare --mount --map-root-user /bin/true >>>>>> >>>>>> then this will succeed. The new option causes unshare to create a >>>>>> user namespace in which the unprivileged user is mapped to UID/GID 0, >>>>>> and so gains all privileges (inside the namespace), the user is then >>>>>> able to create the mount namespace as required. >>>>>> >>>>>> So, how does this relate to GDB? >>>>>> >>>>>> When a user attaches to a process running in a separate mount >>>>>> namespace, GDB makes use of a separate helper process (see >>>>>> linux_mntns_get_helper in nat/linux-namespaces.c), which will then use >>>>>> the `setns` function to enter (or try to enter) the mount namespace of >>>>>> the process GDB is attaching too. The helper process will then handle >>>>>> file I/O requests received from GDB, and return the results back to >>>>>> GDB, this allows GDB to access files within the mount namespace. >>>>>> >>>>>> The problem here is that, switching to a mount namespace requires that >>>>>> a process hold CAP_SYS_CHROOT and CAP_SYS_ADMIN capabilities within >>>>>> its user namespace (actually it's a little more complex, see 'man 2 >>>>>> setns'). Assuming GDB is running as an unprivileged user, then GDB >>>>>> will not have the required permissions. >>>>>> >>>>>> However, if GDB enters the user namespace that the `unshare` process >>>>>> created, then the current user will be mapped to UID/GID 0, and will >>>>>> have the required permissions. >>>>>> >>>>>> And so, this patch extends linux_mntns_access_fs (in >>>>>> nat/linux-namespace.c) to first try and switch to the user namespace >>>>>> of the inferior before trying to switch to the mount namespace. If >>>>>> the inferior does have a user namespace, and does have elevated >>>>>> privileges within that namespace, then this first switch by GDB will >>>>>> mean that the second step, into the mount namespace, will succeed. >>>>>> >>>>>> If there is no user namespace, or the inferior doesn't have elevated >>>>>> privileges within the user namespace, then the switch into the mount >>>>>> namespace will fail, just as it currently does, and the user will need >>>>>> to give elevated privileges to GDB via some other mechanism (e.g. run >>>>>> as root). >>>>>> >>>>>> This work was originally posted here: >>>>>> >>>>>> https://inbox.sourceware.org/gdb-patches/20230321120126.1418012-1-benjamin@sipsolutions.net >>>>>> >>>>>> I (Andrew Burgess) have made some cleanups to the code to comply with >>>>>> GDB's coding standard, and the test is entirely mine. This commit >>>>>> message is also entirely mine -- the original message was very terse >>>>>> and required the reader to understand how the various namespaces >>>>>> work and interact. The above is my attempt to document what I now >>>>>> understand about the problem being fixed. >>>>>> >>>>>> I've left the original author in place as the core of the GDB change >>>>>> itself is largely as originally presented, but any inaccuracies in the >>>>>> commit message, or problems with the test, are all mine. >>>>>> >>>>>> Co-Authored-by: Andrew Burgess >>>>> >>>>> I've pushed this patch. >>>>> >>>> >>>> The new test-case fails on arm32 (Linaro CI reported this, and I was >>>> able to reproduce) due to insufficient permissions: >>>> ... >>>> (gdb) attach 184732 >>>> Attaching to process 184732 >>>> warning: process 184732 is a zombie - the process has already terminated >>>> ptrace: Operation not permitted. >>>> (gdb) FAIL: gdb.base/user-namespace-attach.exp: flags=--mount >>>> --map-root-user: attach to inferior >>>> ... >>>> >>>> In essence, the test-case assumes: >>>> ... >>>> $ unshare --mount --map-root-user /bin/true; echo $? >>>> 0 >>>> ... >>>> but we get instead: >>>> ... >>>> $ unshare --mount --map-root-user /bin/true; echo $? >>>> unshare: unshare failed: Operation not permitted >>>> 1 >>>> ... >>>> >>>> Filed here ( https://sourceware.org/bugzilla/show_bug.cgi?id=33108 ). >>> >>> Hi! >>> >>> Thanks for raising this issue. >>> >>> What do you think to the patch below? >>> >>> I've tested this by passing a bogus flag to `unshare`, e.g. "unshare >>> -blahblah", which has the same effect of causing the `unshare` process >>> to exit immediately with an exit code of 1. I now see the test reported >>> as unsupported. >>> >> >> Hi Andrew, >> >> thanks for picking this up. >> >> FWIW, the problem with this solution is that a timeout now looks like >> unsupported. >> >> More concretely, by doing this (on x86_64-linux, where the test-case >> passes for me): >> ... >> diff --git a/gdb/testsuite/gdb.base/user-namespace-attach.exp >> b/gdb/testsuite/gdb.base/user >> -namespace-attach.exp >> index 01f3dae1693..c5ec5ef6369 100644 >> --- a/gdb/testsuite/gdb.base/user-namespace-attach.exp >> +++ b/gdb/testsuite/gdb.base/user-namespace-attach.exp >> @@ -66,6 +66,7 @@ proc run_test { flags } { >> } >> >> set inferior_pid [spawn_id_get_pid $inferior_spawn_id] >> + sleep 90 >> >> clean_restart >> >> ... >> I trigger the timeout of 60 seconds in the exec, and with your patch get: >> ... >> === gdb Summary === >> >> # of unsupported tests 3 >> ... >> but without your patch I get: >> ... >> # of unexpected failures 6 >> ... >> >> I don't think it's terribly important though. >> >> You could try the approach I proposed in the PR, or you could pursue >> this one. >> >> In the latter case, please add a comment that a timeout may trigger the >> same message. > > You make a good point. I think your suggestion is probably the best > approach then. How about the patch below? > LGTM. I've also tested it on x86_64-linux, where the test-case still passes, and on arm-linux, where the test-case now results in 3 times unsupported. Thanks, - Tom > Thanks, > Andrew > > --- > > 4d0265f72da gdb/testsuite: handle failure to start process for later attach test [Andrew Burgess (2 minutes ago)] > > diff --git a/gdb/testsuite/gdb.base/user-namespace-attach.exp b/gdb/testsuite/gdb.base/user-namespace-attach.exp > index 9936bb998eb..741093c2c14 100644 > --- a/gdb/testsuite/gdb.base/user-namespace-attach.exp > +++ b/gdb/testsuite/gdb.base/user-namespace-attach.exp > @@ -56,10 +56,22 @@ proc run_test { flags } { > set prefix "" > } > > + set unshare_cmd "unshare $flags" > > + # Run '/bin/true' using UNSHARE_CMD. If the flags in UNSHARE_CMD > + # aren't supported then this will fail, this means we shouldn't > + # spawn the command with our test executable and try attaching. > + # > + # This will also fail if /bin/true isn't present, or doesn't work > + # as we expect. But this should be fine for many targets. > + set res [remote_exec target "$unshare_cmd /bin/true"] > + if { [lindex $res 0] != 0 } { > + unsupported "unshare flags not supported" > + return > + } > > set inferior_spawn_id \ > - [spawn_wait_for_attach [list "unshare $flags $::binfile"]] > + [spawn_wait_for_attach [list "$unshare_cmd $::binfile"]] > if { $inferior_spawn_id == -1 } { > unsupported "failed to spawn for attach" > return >