On Mon, 28 Oct 2024 14:43:57 -0700 Kalesh Singh kaleshsingh@google.com wrote:

[1] and [2] introduced a new gid mount options that could apply to a group to all entries in tracefs.

Document this in the tracing readme.

[1] https://lore.kernel.org/r/20211208075720.4855d180@gandalf.local.home/T/#u [2] https://lore.kernel.org/r/20211207171729.2a54e1b3@gandalf.local.home/T/#u

Your patch series is backwards. The first patch should be the fix, the second be this patch and the last one is the test case.

You should reference commit IDs and not links.

Commit ee7f3666995d ("tracefs: Have new files inherit the ownership of their parent") and commit 48b27b6b5191 ("tracefs: Set all files to the same group ownership as the mount option") introduced a new gid..."

-- Steve

Cc: David Howells dhowells@redhat.com Cc: Steven Rostedt rostedt@goodmis.org Cc: Masami Hiramatsu mhiramat@kernel.org Signed-off-by: Kalesh Singh kaleshsingh@google.com

---

kernel/trace/trace.c | 4 ++++ 1 file changed, 4 insertions(+)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index a8f52b6527ca..2b64b3ec67d9 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -5501,6 +5501,10 @@ static const struct file_operations tracing_iter_fops = { static const char readme_msg[] = "tracing mini-HOWTO:\n\n"

• "By default tracefs removes all OTH file permission bits.\n"
• "When mounting tracefs an optional group id can be specified\n"
• "which adds the group to every directory and file in tracefs:\n\n"
• "\t e.g. mount -t tracefs [-o [gid=<gid>]] nodev /sys/kernel/tracing\n\n" "# echo 0 > tracing_on : quick way to disable tracing\n" "# echo 1 > tracing_on : quick way to re-enable tracing\n\n" " Important files:\n"

On Mon, 28 Oct 2024 14:43:58 -0700 Kalesh Singh kaleshsingh@google.com wrote:

Add test to check the tracefs gid mount option is applied correctly

./ftracetest test.d/00basic/mount_options.tc

Use the new readme string "[gid=<gid>] as a requirement and also update test_ownership.tc requirements to use this.

mount_options.tc will fail currently, this is fixed by the subsequent patch in this series.

Test cases should never be added when they can fail. They should always come after the fix is applied. But it appears that you check the README to make sure that it does work and not fail.

I'll take a look at these patches in more detail later.

Thanks,

-- Steve

Cc: David Howells dhowells@redhat.com Cc: Steven Rostedt rostedt@goodmis.org Cc: Masami Hiramatsu mhiramat@kernel.org Signed-off-by: Kalesh Singh kaleshsingh@google.com

---

.../ftrace/test.d/00basic/mount_options.tc | 101 ++++++++++++++++++ .../ftrace/test.d/00basic/test_ownership.tc | 16 +-- .../testing/selftests/ftrace/test.d/functions | 25 +++++ 3 files changed, 129 insertions(+), 13 deletions(-) create mode 100644 tools/testing/selftests/ftrace/test.d/00basic/mount_options.tc

diff --git a/tools/testing/selftests/ftrace/test.d/00basic/mount_options.tc b/tools/testing/selftests/ftrace/test.d/00basic/mount_options.tc new file mode 100644 index 000000000000..b8aff85ec259 --- /dev/null +++ b/tools/testing/selftests/ftrace/test.d/00basic/mount_options.tc @@ -0,0 +1,101 @@ +#!/bin/sh +# SPDX-License-Identifier: GPL-2.0 +# description: Test tracefs GID mount option +# requires: "[gid=<gid>]":README

+fail() {

• local msg="$1"
• echo "FAILED: $msg"
• exit_fail

+}

+find_alternate_gid() {

• local original_gid="$1"
• tac /etc/group | grep -v ":$original_gid:" | head -1 | cut -d: -f3

+}

+mount_tracefs_with_options() {

• local mount_point="$1"
• local options="$2"
• mount -t tracefs -o "$options" nodev "$mount_point"
• setup

+}

+unmount_tracefs() {

• local mount_point="$1"
• # Need to make sure the mount isn't busy so that we can umount it
• (cd $mount_point; finish_ftrace;)
• cleanup

+}

+create_instance() {

• local mount_point="$1"
• local instance="$mount_point/instances/$(mktemp -u test-XXXXXX)"
• mkdir "$instance"
• echo "$instance"

+}

+remove_instance() {

• local instance="$1"
• rmdir "$instance"

+}

+check_gid() {

• local mount_point="$1"
• local expected_gid="$2"
• echo "Checking permission group ..."
• cd "$mount_point"
• for file in "." "events" "events/sched" "events/sched/sched_switch" "events/sched/sched_switch/enable"; do

• local gid=`stat -c "%g" $file`
  

• if [ "$gid" -ne "$expected_gid" ]; then
  

• 	cd - # Return to the previous working direcotry (tracefs root)
  

• 	fail "$(realpath $file): Expected group $expected_gid; Got group $gid"
  

• fi
  

• done
• cd - # Return to the previous working direcotry (tracefs root)

+}

+test_gid_mount_option() {

• local mount_point=$(get_mount_point)
• local mount_options=$(get_mnt_options "$mount_point")
• local original_group=$(stat -c "%g" .)
• local other_group=$(find_alternate_gid "$original_group")
• # Set up mount options with new GID for testing
• local new_options=`echo "$mount_options" | sed -e "s/gid=[0-9]*/gid=$other_group/"`
• if [ "$new_options" = "$mount_options" ]; then

• new_options="$mount_options,gid=$other_group"
  

• mount_options="$mount_options,gid=$original_group"
  

• fi
• # Unmount existing tracefs instance and mount with new GID
• unmount_tracefs "$mount_point"
• mount_tracefs_with_options "$mount_point" "$new_options"
• check_gid "$mount_point" "$other_group"
• # Check that files created after the mount inherit the GID
• local instance=$(create_instance "$mount_point")
• check_gid "$instance" "$other_group"
• remove_instance "$instance"
• # Unmount and remount with the original GID
• unmount_tracefs "$mount_point"
• mount_tracefs_with_options "$mount_point" "$mount_options"
• check_gid "$mount_point" "$original_group"

+}

+test_gid_mount_option

+exit 0 diff --git a/tools/testing/selftests/ftrace/test.d/00basic/test_ownership.tc b/tools/testing/selftests/ftrace/test.d/00basic/test_ownership.tc index 094419e190c2..e71cc3ad0bdf 100644 --- a/tools/testing/selftests/ftrace/test.d/00basic/test_ownership.tc +++ b/tools/testing/selftests/ftrace/test.d/00basic/test_ownership.tc @@ -1,24 +1,14 @@ #!/bin/sh # SPDX-License-Identifier: GPL-2.0 # description: Test file and directory ownership changes for eventfs +# requires: "[gid=<gid>]":README original_group=`stat -c "%g" .` original_owner=`stat -c "%u" .` -mount_point=`stat -c '%m' .` +local mount_point=$(get_mount_point) -# If stat -c '%m' does not work (e.g. busybox) or failed, try to use the -# current working directory (which should be a tracefs) as the mount point. -if [ ! -d "$mount_point" ]; then

• if mount | grep -qw $PWD ; then

• mount_point=$PWD
  

• else

• # If PWD doesn't work, that is an environmental problem.
  

• exit_unresolved
  

• fi

-fi

-mount_options=`mount | grep "$mount_point" | sed -e 's/.*((.*)).*/\1/'` +mount_options=$(get_mnt_options "$mount_point") # find another owner and group that is not the original other_group=`tac /etc/group | grep -v ":$original_group:" | head -1 | cut -d: -f3` diff --git a/tools/testing/selftests/ftrace/test.d/functions b/tools/testing/selftests/ftrace/test.d/functions index 779f3e62ec90..84d6a9c7ad67 100644 --- a/tools/testing/selftests/ftrace/test.d/functions +++ b/tools/testing/selftests/ftrace/test.d/functions @@ -193,3 +193,28 @@ ftrace_errlog_check() { # err-prefix command-with-error-pos-by-^ command-file # " Command: " and "^\n" => 13 test $(expr 13 + $pos) -eq $N }

+# Helper to get the tracefs mount point +get_mount_point() {

• local mount_point=`stat -c '%m' .`
• # If stat -c '%m' does not work (e.g. busybox) or failed, try to use the
• # current working directory (which should be a tracefs) as the mount point.
• if [ ! -d "$mount_point" ]; then

• if mount | grep -qw "$PWD"; then
  

• 	mount_point=$PWD
  

• else
  

• 	# If PWD doesn't work, that is an environmental problem.
  

• 	exit_unresolved
  

• fi
  

• fi
• echo "$mount_point"

+}

+# Helper function to retrieve mount options for a given mount point +get_mnt_options() {

• local mnt_point="$1"
• local opts=$(mount | grep -m1 "$mnt_point" | sed -e 's/.*((.*)).*/\1/')
• echo "$opts"

+} \ No newline at end of file

On Mon, Oct 28, 2024 at 4:23 PM Kalesh Singh kaleshsingh@google.com wrote:

On Mon, Oct 28, 2024 at 4:14 PM Steven Rostedt rostedt@goodmis.org wrote:

...

On Mon, 28 Oct 2024 14:43:58 -0700 Kalesh Singh kaleshsingh@google.com wrote:

...

Add test to check the tracefs gid mount option is applied correctly

./ftracetest test.d/00basic/mount_options.tc

Use the new readme string "[gid=<gid>] as a requirement and also update test_ownership.tc requirements to use this.

mount_options.tc will fail currently, this is fixed by the subsequent patch in this series.

Test cases should never be added when they can fail. They should always come after the fix is applied. But it appears that you check the README to make sure that it does work and not fail.

I'll take a look at these patches in more detail later.

Hi Steve,

Thank you for the quick reviews, please feel free to ignore until you are back.

I'll address these comments and resend a v2.

I've posted v2 at: https://lore.kernel.org/r/20241030171928.4168869-1-kaleshsingh@google.com/

Thanks, Kalesh

Thanks, Kalesh

...

Thanks,

-- Steve

...

Cc: David Howells dhowells@redhat.com Cc: Steven Rostedt rostedt@goodmis.org Cc: Masami Hiramatsu mhiramat@kernel.org Signed-off-by: Kalesh Singh kaleshsingh@google.com

---

.../ftrace/test.d/00basic/mount_options.tc | 101 ++++++++++++++++++ .../ftrace/test.d/00basic/test_ownership.tc | 16 +-- .../testing/selftests/ftrace/test.d/functions | 25 +++++ 3 files changed, 129 insertions(+), 13 deletions(-) create mode 100644 tools/testing/selftests/ftrace/test.d/00basic/mount_options.tc

diff --git a/tools/testing/selftests/ftrace/test.d/00basic/mount_options.tc b/tools/testing/selftests/ftrace/test.d/00basic/mount_options.tc new file mode 100644 index 000000000000..b8aff85ec259 --- /dev/null +++ b/tools/testing/selftests/ftrace/test.d/00basic/mount_options.tc @@ -0,0 +1,101 @@ +#!/bin/sh +# SPDX-License-Identifier: GPL-2.0 +# description: Test tracefs GID mount option +# requires: "[gid=<gid>]":README

+fail() {

• local msg="$1"
  

• echo "FAILED: $msg"
  

• exit_fail
  

+}

+find_alternate_gid() {

• local original_gid="$1"
  

• tac /etc/group | grep -v ":$original_gid:" | head -1 | cut -d: -f3
  

+}

+mount_tracefs_with_options() {

• local mount_point="$1"
  

• local options="$2"
  

• mount -t tracefs -o "$options" nodev "$mount_point"
  

• setup
  

+}

+unmount_tracefs() {

• local mount_point="$1"
  

• # Need to make sure the mount isn't busy so that we can umount it
  

• (cd $mount_point; finish_ftrace;)
  

• cleanup
  

+}

+create_instance() {

• local mount_point="$1"
  

• local instance="$mount_point/instances/$(mktemp -u test-XXXXXX)"
  

• mkdir "$instance"
  

• echo "$instance"
  

+}

+remove_instance() {

• local instance="$1"
  

• rmdir "$instance"
  

+}

+check_gid() {

• local mount_point="$1"
  

• local expected_gid="$2"
  

• echo "Checking permission group ..."
  

• cd "$mount_point"
  

• for file in "." "events" "events/sched" "events/sched/sched_switch" "events/sched/sched_switch/enable"; do
  

•         local gid=`stat -c "%g" $file`
  

•         if [ "$gid" -ne "$expected_gid" ]; then
  

•                 cd - # Return to the previous working direcotry (tracefs root)
  

•                 fail "$(realpath $file): Expected group $expected_gid; Got group $gid"
  

•         fi
  

• done
  

• cd - # Return to the previous working direcotry (tracefs root)
  

+}

+test_gid_mount_option() {

• local mount_point=$(get_mount_point)
  

• local mount_options=$(get_mnt_options "$mount_point")
  

• local original_group=$(stat -c "%g" .)
  

• local other_group=$(find_alternate_gid "$original_group")
  

• # Set up mount options with new GID for testing
  

• local new_options=`echo "$mount_options" | sed -e "s/gid=[0-9]*/gid=$other_group/"`
  

• if [ "$new_options" = "$mount_options" ]; then
  

•         new_options="$mount_options,gid=$other_group"
  

•         mount_options="$mount_options,gid=$original_group"
  

• fi
  

• # Unmount existing tracefs instance and mount with new GID
  

• unmount_tracefs "$mount_point"
  

• mount_tracefs_with_options "$mount_point" "$new_options"
  

• check_gid "$mount_point" "$other_group"
  

• # Check that files created after the mount inherit the GID
  

• local instance=$(create_instance "$mount_point")
  

• check_gid "$instance" "$other_group"
  

• remove_instance "$instance"
  

• # Unmount and remount with the original GID
  

• unmount_tracefs "$mount_point"
  

• mount_tracefs_with_options "$mount_point" "$mount_options"
  

• check_gid "$mount_point" "$original_group"
  

+}

+test_gid_mount_option

+exit 0 diff --git a/tools/testing/selftests/ftrace/test.d/00basic/test_ownership.tc b/tools/testing/selftests/ftrace/test.d/00basic/test_ownership.tc index 094419e190c2..e71cc3ad0bdf 100644 --- a/tools/testing/selftests/ftrace/test.d/00basic/test_ownership.tc +++ b/tools/testing/selftests/ftrace/test.d/00basic/test_ownership.tc @@ -1,24 +1,14 @@ #!/bin/sh # SPDX-License-Identifier: GPL-2.0 # description: Test file and directory ownership changes for eventfs +# requires: "[gid=<gid>]":README

original_group=`stat -c "%g" .` original_owner=`stat -c "%u" .`

-mount_point=`stat -c '%m' .` +local mount_point=$(get_mount_point)

-# If stat -c '%m' does not work (e.g. busybox) or failed, try to use the -# current working directory (which should be a tracefs) as the mount point. -if [ ! -d "$mount_point" ]; then

• if mount | grep -qw $PWD ; then
  

•         mount_point=$PWD
  

• else
  

•         # If PWD doesn't work, that is an environmental problem.
  

•         exit_unresolved
  

• fi
  

-fi

-mount_options=`mount | grep "$mount_point" | sed -e 's/.*((.*)).*/\1/'` +mount_options=$(get_mnt_options "$mount_point")

# find another owner and group that is not the original other_group=`tac /etc/group | grep -v ":$original_group:" | head -1 | cut -d: -f3` diff --git a/tools/testing/selftests/ftrace/test.d/functions b/tools/testing/selftests/ftrace/test.d/functions index 779f3e62ec90..84d6a9c7ad67 100644 --- a/tools/testing/selftests/ftrace/test.d/functions +++ b/tools/testing/selftests/ftrace/test.d/functions @@ -193,3 +193,28 @@ ftrace_errlog_check() { # err-prefix command-with-error-pos-by-^ command-file # " Command: " and "^\n" => 13 test $(expr 13 + $pos) -eq $N }

+# Helper to get the tracefs mount point +get_mount_point() {

• local mount_point=`stat -c '%m' .`
  

• # If stat -c '%m' does not work (e.g. busybox) or failed, try to use the
  

• # current working directory (which should be a tracefs) as the mount point.
  

• if [ ! -d "$mount_point" ]; then
  

•         if mount | grep -qw "$PWD"; then
  

•                 mount_point=$PWD
  

•         else
  

•                 # If PWD doesn't work, that is an environmental problem.
  

•                 exit_unresolved
  

•         fi
  

• fi
  

• echo "$mount_point"
  

+}

+# Helper function to retrieve mount options for a given mount point +get_mnt_options() {

• local mnt_point="$1"
  

• local opts=$(mount | grep -m1 "$mnt_point" | sed -e 's/.*(\(.*\)).*/\1/')
  

• echo "$opts"
  

+} \ No newline at end of file

On 10/28/24 4:43 PM, Kalesh Singh wrote:

Commit 78ff64081949 ("vfs: Convert tracefs to use the new mount API") tracefs to use the new mount APIs caused mounting with the gid=<gid> option to not take effect.

Or any other mount options. I'm sure this isn't unique to gid, right? So, might want to fix the commit title.

The tracefs superblock can be updated from multiple paths: - on fs_initcall() to init_trace_printk_function_export() - form a work queue to initialize eventfs tracer_init_tracefs_work_func() - fsconfig() syscall to mount of remount sysfs

The tracefs super block root inode gets created early on in init_trace_printk_function_export().

With the new mount API tracefs effectively uses get_tree_single() instead of the old API mount_single().

Previously, mount_single() ensured that the options are alway applied to the superblock root inode: (1) If the root inode didn't exist, called fill_super() to create it and apply the options. (2) If the root inode exists, called reconfigure_single() which effectively called tracefs_apply_options() to parse and apply options to the subperblock's fs_info and inode and remount eventfs (if necessary)

On the other hand, get_tree_single() effectively calls vfs_get_super() which: (3) If the root inode doesn't exists calls fill_super() to create it and apply the options. (4) If the root inode already exists, updates the fs_context root with the superblock's root inode.

I'm honestly a little lost here, but given the differences between mount_single() and get_tree_single() - are other get_tree_single() users similarly broken?

Should get_tree_single() just be calling reconfigure_single() internally like mount_single() did? The comment in reconfigure_single() confuses me.

(4) above is always the case for tracefs mounts, since the super block's root inode will already be created by init_trace_printk_function_export().

this reminds me a little of

commit a6097180d884ddab769fb25588ea8598589c218c Author: NeilBrown neilb@suse.de Date: Mon Jan 17 09:07:26 2022 +1100

devtmpfs regression fix: reconfigure on each mount

This means that the gid mount option gets ignored: - Since it isn't applied to the super block's root inode, it doesn't get inherited by the children. - Since eventfs is initialized from form a separate work queue and before call to mount with the options, and it doesn't get remounted for mount.

Ensure that the mount options are applied to the super block and eventfs is remounted to respect the new mount options.

[1] https://lore.kernel.org/r/536e99d3-345c-448b-adee-a21389d7ab4b@redhat.com/

Fixes: 78ff64081949 ("vfs: Convert tracefs to use the new mount API") Cc: David Howells dhowells@redhat.com Cc: Steven Rostedt rostedt@goodmis.org Cc: Masami Hiramatsu mhiramat@kernel.org Signed-off-by: Kalesh Singh kaleshsingh@google.com

---

fs/tracefs/inode.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/fs/tracefs/inode.c b/fs/tracefs/inode.c index 1748dff58c3b..cfc614c638da 100644 --- a/fs/tracefs/inode.c +++ b/fs/tracefs/inode.c @@ -392,6 +392,9 @@ static int tracefs_reconfigure(struct fs_context *fc) struct tracefs_fs_info *sb_opts = sb->s_fs_info; struct tracefs_fs_info *new_opts = fc->s_fs_info;

• if (!new_opts)

• return 0;
  

Can this really happen?

• sync_filesystem(sb); /* structure copy of new mount options to sb */ *sb_opts = *new_opts;

FWIW doing this as a structure copy was probably a terrible choice on my part. :(

@@ -478,14 +481,17 @@ static int tracefs_fill_super(struct super_block *sb, struct fs_context *fc) sb->s_op = &tracefs_super_operations; sb->s_d_op = &tracefs_dentry_operations;

• tracefs_apply_options(sb, false);
• return 0;

} static int tracefs_get_tree(struct fs_context *fc) {

• return get_tree_single(fc, tracefs_fill_super);

• int err = get_tree_single(fc, tracefs_fill_super);
• if (err)

• return err;
  

• return tracefs_reconfigure(fc);

} static void tracefs_free_fc(struct fs_context *fc)