proc/sysctl: make protected_* world readable

protected_* files have 600 permissions which prevents non-superuser from
reading them.

Container like "AWS greengrass" refuse to launch unless
protected_hardlinks and protected_symlinks are set.  When containers like
these run with "userns-remap" or "--user" mapping container's root to
non-superuser on host, they fail to run due to denied read access to these
files.

As these protections are hardly a secret, and do not possess any security
risk, making them world readable.

Though above greengrass usecase needs read access to only
protected_hardlinks and protected_symlinks files, setting all other
protected_* files to 644 to keep consistency.

Link: http://lkml.kernel.org/r/20200709235115.56954-1-jpitti@cisco.com
Fixes: 800179c9b8a1 ("fs: add link restrictions")
Signed-off-by: Julius Hemanth Pitti <jpitti@cisco.com>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Iurii Zaikin <yzaikin@google.com>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 14edf84cc571f5c19b8eec330719e3f36807f19a..453438c43b021df1c8c9501bd430924be4a1db21 100644 (file)
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -3252,7 +3252,7 @@ static struct ctl_table fs_table[] = {
                .procname       = "protected_symlinks",
                .data           = &sysctl_protected_symlinks,
                .maxlen         = sizeof(int),
-               .mode           = 0600,
+               .mode           = 0644,
                .proc_handler   = proc_dointvec_minmax,
                .extra1         = SYSCTL_ZERO,
                .extra2         = SYSCTL_ONE,
@@ -3261,7 +3261,7 @@ static struct ctl_table fs_table[] = {
                .procname       = "protected_hardlinks",
                .data           = &sysctl_protected_hardlinks,
                .maxlen         = sizeof(int),
-               .mode           = 0600,
+               .mode           = 0644,
                .proc_handler   = proc_dointvec_minmax,
                .extra1         = SYSCTL_ZERO,
                .extra2         = SYSCTL_ONE,
@@ -3270,7 +3270,7 @@ static struct ctl_table fs_table[] = {
                .procname       = "protected_fifos",
                .data           = &sysctl_protected_fifos,
                .maxlen         = sizeof(int),
-               .mode           = 0600,
+               .mode           = 0644,
                .proc_handler   = proc_dointvec_minmax,
                .extra1         = SYSCTL_ZERO,
                .extra2         = &two,
@@ -3279,7 +3279,7 @@ static struct ctl_table fs_table[] = {
                .procname       = "protected_regular",
                .data           = &sysctl_protected_regular,
                .maxlen         = sizeof(int),
-               .mode           = 0600,
+               .mode           = 0644,
                .proc_handler   = proc_dointvec_minmax,
                .extra1         = SYSCTL_ZERO,
                .extra2         = &two,