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From 64fa6f059ae0b491fdb52c7375d59774ff9c237a Mon Sep 17 00:00:00 2001
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From: =?UTF-8?q?Zbigniew=20J=C4=99drzejewski-Szmek?= <zbyszek@in.waw.pl>
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Date: Tue, 15 Mar 2022 16:35:47 +0100
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Subject: [PATCH] shared/install: do not try to resolve symlinks outside of
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 root directory
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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I linked a file as root, so I had a symlink /root/test.service ← /etc/systemd/system/test.service.
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To my surpise, when running test-systemctl-enable, it failed with a cryptic EACCES.
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The previous commit made the logs a bit better. Strace shows that we
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were trying to follow the symlink without taking --root into account.
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It seems that this bug was introduced in 66a19d85a533b15ed32f4066ec880b5a8c06babd:
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before it, we'd do readlink_malloc(), which returned a path relative to root. But
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we only used that path for checking if the path is in remove_symlinks_to set, which
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contains relative paths. So if the path was relative, we'd get a false-negative
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answer, but we didn't go outside of the root. (We need to canonicalize the symlink
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to get a consistent answer.) But after 66a19 we use chase_symlinks(), without taking
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root into account which is completely bogus.
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(cherry picked from commit 40276314afc4fb5c35c6b3da3e6185af6ed3886b)
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Related: #2082131
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---
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 src/shared/install.c | 2 +-
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 1 file changed, 1 insertion(+), 1 deletion(-)
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diff --git a/src/shared/install.c b/src/shared/install.c
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index ce045d02be..ad0238ab50 100644
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--- a/src/shared/install.c
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+++ b/src/shared/install.c
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@@ -612,7 +612,7 @@ static int remove_marked_symlinks_fd(
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                                 return -ENOMEM;
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                         path_simplify(p);
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-                        q = chase_symlinks(p, NULL, CHASE_NONEXISTENT, &dest, NULL);
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+                        q = chase_symlinks(p, lp->root_dir, CHASE_NONEXISTENT, &dest, NULL);
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                         if (q == -ENOENT)
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                                 continue;
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                         if (q < 0) {