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ANDROID: regression introduced override_creds=off

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Solve a regression introduced by
commit 272fcd1ca7ceb252b1c3a2961110c7c1722707cf
("ANDROID: overlayfs: override_creds=off option bypass creator_cred")
where a crash is observed a crash in ovl_create_or_link() when a
simple re-direction command in vendor directory.

/vendor/bin/<Any test> > /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 <salyzyn@google.com>
Tested-by: Rishabh/Jeevan <jshriram@qualcomm.corp-partner.google.com>
Bug: 140816499
Change-Id: Icd0d9be82fc57af5ead1eeab99f79adf3adf62ef
This commit is contained in:
Mark Salyzyn 2019-09-13 08:25:31 -07:00
parent c890d5ab00
commit f1bf45bfb9
1 changed files with 5 additions and 3 deletions
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8
fs/overlayfs/dir.c
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@ -469,7 +469,7 @@ static int ovl_create_or_link(struct dentry *dentry, struct inode *inode,
bool origin)
{
int err;
const struct cred *old_cred;
const struct cred *old_cred, *hold_cred = NULL;
struct cred *override_cred;
struct dentry *parent = dentry->d_parent;
@ -504,7 +504,7 @@ static int ovl_create_or_link(struct dentry *dentry, struct inode *inode,
goto out_revert_creds;
}
}
put_cred(override_creds(override_cred));
hold_cred = override_creds(override_cred);
put_cred(override_cred);
if (!ovl_dentry_is_whiteout(dentry))
@ -515,7 +515,9 @@ static int ovl_create_or_link(struct dentry *dentry, struct inode *inode,
hardlink);
}
out_revert_creds:
ovl_revert_creds(old_cred);
ovl_revert_creds(old_cred ?: hold_cred);
if (old_cred && hold_cred)
put_cred(hold_cred);
if (!err) {
struct inode *realinode = d_inode(ovl_dentry_upper(dentry));