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Tue, 16 Sep 2025 14:11:56 -0700 (PDT) Received: from crl-3.node2.local ([125.63.65.162]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-b54a36c78b5sm15524738a12.21.2025.09.16.14.11.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 16 Sep 2025 14:11:55 -0700 (PDT) From: Kriish Sharma To: agruenba@redhat.com Cc: gfs2@lists.linux.dev, linux-kernel@vger.kernel.org, Kriish Sharma , syzbot+fa7122891ab9e0bbc6a7@syzkaller.appspotmail.com Subject: [PATCH] gfs2: avoid %pS in pr_err() fallback to prevent vsnprintf crash Date: Tue, 16 Sep 2025 21:11:08 +0000 Message-Id: <20250916211108.1243390-1-kriish.sharma2006@gmail.com> X-Mailer: git-send-email 2.34.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable While debugging a syzbot report, I found that the %pS format in dump_holder() can trigger a crash when we end up in the pr_err() fallback path. This happens because %pS goes through symbol resolution inside vsnprintf, and in this case that isn=E2=80=99t always safe. I switched the seq_file case to continue using %pS, since it is useful there, but changed the pr_err() path to use %p instead. This way we still print a valid pointer address without risking a kernel oops from within printk itself. The idea is to keep the debugging value but make it more robust. Fixes: 590b221ed425 ("Add linux-next specific files for 20250912") Reported-by: syzbot+fa7122891ab9e0bbc6a7@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=3Dfa7122891ab9e0bbc6a7 Signed-off-by: Kriish Sharma --- fs/gfs2/glock.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c index b677c0e6b9ab..903844a6ebbc 100644 --- a/fs/gfs2/glock.c +++ b/fs/gfs2/glock.c @@ -2284,10 +2284,18 @@ static void dump_holder(struct seq_file *seq, const= struct gfs2_holder *gh, if (gh_owner) comm =3D gh_owner->comm; } - gfs2_print_dbg(seq, "%s H: s:%s f:%s e:%d p:%ld [%s] %pS\n", - fs_id_buf, state2str(gh->gh_state), - hflags2str(flags_buf, gh->gh_flags, gh->gh_iflags), - gh->gh_error, (long)owner_pid, comm, (void *)gh->gh_ip); + if (seq) { + gfs2_print_dbg(seq, "%s H: s:%s f:%s e:%d p:%ld [%s] %pS\n", + fs_id_buf, state2str(gh->gh_state), + hflags2str(flags_buf, gh->gh_flags, gh->gh_iflags), + gh->gh_error, (long)owner_pid, comm, (void *)gh->gh_ip); + } else { + gfs2_print_dbg(seq, "%s H: s:%s f:%s e:%d p:%ld [%s] %p\n", + fs_id_buf, state2str(gh->gh_state), + hflags2str(flags_buf, gh->gh_flags, gh->gh_iflags), + gh->gh_error, (long)owner_pid, comm, + (void *)gh->gh_ip); + } rcu_read_unlock(); } =20 --=20 2.34.1