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From 26f96ca10ad0ec5da9b05b99de1e1ccea15a11be Mon Sep 17 00:00:00 2001
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From: "djm@openbsd.org" <djm@openbsd.org>
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Date: Fri, 15 Jun 2018 07:01:11 +0000
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Subject: [PATCH] upstream: invalidate supplemental group cache used by
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temporarily_use_uid() when the target uid differs; could cause failure to
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read authorized_keys under some configurations. patch by Jakub Jelen via
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bz2873; ok dtucker, markus
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OpenBSD-Commit-ID: 48a345f0ee90f6c465a078eb5e89566b23abd8a1
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---
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 uidswap.c | 8 ++++++--
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 1 file changed, 6 insertions(+), 2 deletions(-)
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diff --git a/uidswap.c b/uidswap.c
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index 8bf6b244e..1430b822a 100644
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--- a/uidswap.c
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+++ b/uidswap.c
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@@ -49,6 +49,7 @@ static gid_t	saved_egid = 0;
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 /* Saved effective uid. */
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 static int	privileged = 0;
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 static int	temporarily_use_uid_effective = 0;
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+static uid_t	user_groups_uid;
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 static gid_t	*saved_egroups = NULL, *user_groups = NULL;
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 static int	saved_egroupslen = -1, user_groupslen = -1;
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@@ -92,10 +93,11 @@ temporarily_use_uid(struct passwd *pw)
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 			fatal("getgroups: %.100s", strerror(errno));
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 	} else { /* saved_egroupslen == 0 */
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 		free(saved_egroups);
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+		saved_egroups = NULL;
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 	}
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 	/* set and save the user's groups */
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-	if (user_groupslen == -1) {
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+	if (user_groupslen == -1 || user_groups_uid != pw->pw_uid) {
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 		if (initgroups(pw->pw_name, pw->pw_gid) < 0)
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 			fatal("initgroups: %s: %.100s", pw->pw_name,
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 			    strerror(errno));
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@@ -110,7 +112,9 @@ temporarily_use_uid(struct passwd *pw)
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 				fatal("getgroups: %.100s", strerror(errno));
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 		} else { /* user_groupslen == 0 */
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 			free(user_groups);
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+			user_groups = NULL;
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 		}
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+		user_groups_uid = pw->pw_uid;
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 	}
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 	/* Set the effective uid to the given (unprivileged) uid. */
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 	if (setgroups(user_groupslen, user_groups) < 0)
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