From 72c5343cdbc5ec257e45d5387ed7220065c2ecff Mon Sep 17 00:00:00 2001 From: Mark Salyzyn Date: Fri, 13 Sep 2019 08:25:31 -0700 Subject: [PATCH] ANDROID: regression introduced override_creds=off MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Fixes a regression introduced by the series of commits: commit 272fcd1ca7ceb252b1c3a2961110c7c1722707cf ("ANDROID: overlayfs: override_creds=off option bypass creator_cred"), commit aab9adb4b81bcce107dd1783f6ac41dc1abe9f15 ("Merge 4.4.179 into android-4.4") that took in an incomplete, backport of commit 54a07fff4b217607e862b2e1e3fcec32919ad583 ("ovl: fix uid/gid when creating over whiteout") (or upstream commit d0e13f5bbe4be7c8f27736fc40503dcec04b7de0 ("ovl: fix uid/gid when creating over whiteout")) where a crash is observed in ovl_create_or_link() when a simple re-direction command in vendor directory. /vendor/bin/ > /vendor/bin/test_log.txt 2>&1& After further debugging we see that if the output is redirected to a file which doesn’t exist we see this stack: [ 377.382745] ovl_create_or_link+0xac/0x710 [ 377.382745] ovl_create_object+0xb8/0x110 [ 377.382745] ovl_create+0x34/0x40 [ 377.382745] path_openat+0xd44/0x15a8 [ 377.382745] do_filp_open+0x80/0x128 [ 377.382745] do_sys_open+0x140/0x250 [ 377.382745] __arm64_sys_openat+0x2c/0x38 ovl_override_creds returns NULL because the override_cred flag is set to false. This causes ovl_revert_creds also to fail. There is another call to check override_cred in override_cred call which overrides the creds permanently as there no revert_creds associated. So whenever next commit_cred is called we see the crash as the credentials are permanently overridden. Signed-off-by: Mark Salyzyn Tested-by: Rishabh/Jeevan Bug: 140816499 Bug: 109821005 Bug: 112955896 Bug: 127298877 Bug: 137541192 Change-Id: Icd0d9be82fc57af5ead1eeab99f79adf3adf62ef --- fs/overlayfs/dir.c | 17 ++++++++++++----- 1 file changed, 12 insertions(+), 5 deletions(-) diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c index eedacae889b9..b4498b95234c 100644 --- a/fs/overlayfs/dir.c +++ b/fs/overlayfs/dir.c @@ -407,7 +407,7 @@ static int ovl_create_or_link(struct dentry *dentry, int mode, dev_t rdev, if (!ovl_dentry_is_opaque(dentry)) { err = ovl_create_upper(dentry, inode, &stat, link, hardlink); } else { - const struct cred *old_cred; + const struct cred *old_cred, *hold_cred = NULL; struct cred *override_cred; old_cred = ovl_override_creds(dentry->d_sb); @@ -415,15 +415,22 @@ static int ovl_create_or_link(struct dentry *dentry, int mode, dev_t rdev, err = -ENOMEM; override_cred = prepare_creds(); if (override_cred) { - override_cred->fsuid = old_cred->fsuid; - override_cred->fsgid = old_cred->fsgid; - put_cred(override_creds(override_cred)); + const struct cred *our_cred; + + our_cred = old_cred; + if (!our_cred) + our_cred = current_cred(); + override_cred->fsuid = our_cred->fsuid; + override_cred->fsgid = our_cred->fsgid; + hold_cred = override_creds(override_cred); put_cred(override_cred); err = ovl_create_over_whiteout(dentry, inode, &stat, link, hardlink); } - revert_creds(old_cred); + ovl_revert_creds(old_cred ?: hold_cred); + if (old_cred && hold_cred) + put_cred(hold_cred); } if (!err)