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global_macros: trim back various watch* permissions

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Commit dddbaaf1e8 ("update sepolicy
for fs notification hooks") updated global macros, and added
watch, watch_mount, watch_sb, watch_with_perm, and watch_reads
to r_file_perms and r_dir_perms.

In retrospect, the commit was overly permissive and some of the
permissions shouldn't be granted by default. In particular:

1) watch_with_perm: This is only used with fanotify and requires
CAP_SYS_ADMIN. fanotify has limited use cases, including virus scanning
and hierarchical storage management. Granting this by default makes it
harder to audit and understand this powerful capability. In particular,
anti-virus file like monitoring is something which inherently conflicts
with Android app privacy guarantees and would need to be carefully
reviewed.

2) watch_mount & watch_sb: Setting a watch on a mount (FAN_MARK_MOUNT)
or superblock (FAN_MARK_FILESYSTEM) should be extremely unusual.
Granting this by default makes it harder to audit and understand.

Both "watch" and "watch_reads" are retained for now.

References:
* https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=ac5656d8a4cdd93cd2c74355ed12e5617817e0e7
* dddbaaf1e8

Test: compiles
Change-Id: Ib74e7119853eb991e0e9828645c7f9e076b919c4
This commit is contained in:
Nick Kralevich 2019-08-28 12:23:20 -07:00
parent 961bf003d6
commit c4ab8edf74
1 changed files with 2 additions and 2 deletions
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4
public/global_macros
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@ -22,7 +22,7 @@ define(`ipc_class_set', `{ sem msgq shm ipc }')
# Common groupings of permissions.
#
define(`x_file_perms', `{ getattr execute execute_no_trans map }')
define(`r_file_perms', `{ getattr open read ioctl lock map watch watch_mount watch_sb watch_with_perm watch_reads }')
define(`r_file_perms', `{ getattr open read ioctl lock map watch watch_reads }')
define(`w_file_perms', `{ open append write lock map }')
define(`rx_file_perms', `{ r_file_perms x_file_perms }')
define(`ra_file_perms', `{ r_file_perms append }')
@ -30,7 +30,7 @@ define(`rw_file_perms', `{ r_file_perms w_file_perms }')
define(`rwx_file_perms', `{ rw_file_perms x_file_perms }')
define(`create_file_perms', `{ create rename setattr unlink rw_file_perms }')
define(`r_dir_perms', `{ open getattr read search ioctl lock watch watch_mount watch_sb watch_with_perm watch_reads }')
define(`r_dir_perms', `{ open getattr read search ioctl lock watch watch_reads }')
define(`w_dir_perms', `{ open search write add_name remove_name lock }')
define(`ra_dir_perms', `{ r_dir_perms add_name write }')
define(`rw_dir_perms', `{ r_dir_perms w_dir_perms }')