[PATCH 06/10] mm: update coredump logic to correctly use bitmap mm flags

[Lorenzo Stoakes <lorenzo.stoakes@oracle.com>]

The coredump logic is slightly different from other users in that it both
stores mm flags and additionally sets and gets using masks.

Since the MMF_DUMPABLE_* flags must remain as they are for uABI reasons,
and of course these are within the first 32-bits of the flags, it is
reasonable to provide access to these in the same fashion so this logic can
all still keep working as it has been.

Therefore, introduce coredump-specific helpers __mm_flags_get_dumpable()
and __mm_flags_set_mask_dumpable() for this purpose, and update all core
dump users of mm flags to use these.

Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
---
 fs/coredump.c                  |  4 +++-
 fs/exec.c                      |  2 +-
 fs/pidfs.c                     |  7 +++++--
 fs/proc/base.c                 |  8 +++++---
 include/linux/sched/coredump.h | 21 ++++++++++++++++++++-
 5 files changed, 34 insertions(+), 8 deletions(-)

diff --git a/fs/coredump.c b/fs/coredump.c
index fedbead956ed..e5d9d6276990 100644
--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -1103,8 +1103,10 @@ void vfs_coredump(const kernel_siginfo_t *siginfo)
 		 * We must use the same mm->flags while dumping core to avoid
 		 * inconsistency of bit flags, since this flag is not protected
 		 * by any locks.
+		 *
+		 * Note that we only care about MMF_DUMP* flags.
 		 */
-		.mm_flags = mm->flags,
+		.mm_flags = __mm_flags_get_dumpable(mm),
 		.vma_meta = NULL,
 		.cpu = raw_smp_processor_id(),
 	};
diff --git a/fs/exec.c b/fs/exec.c
index 2a1e5e4042a1..dbac0e84cc3e 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1999,7 +1999,7 @@ void set_dumpable(struct mm_struct *mm, int value)
 	if (WARN_ON((unsigned)value > SUID_DUMP_ROOT))
 		return;
 
-	set_mask_bits(&mm->flags, MMF_DUMPABLE_MASK, value);
+	__mm_flags_set_mask_dumpable(mm, value);
 }
 
 SYSCALL_DEFINE3(execve,
diff --git a/fs/pidfs.c b/fs/pidfs.c
index edc35522d75c..5148b7646b7f 100644
--- a/fs/pidfs.c
+++ b/fs/pidfs.c
@@ -357,8 +357,11 @@ static long pidfd_info(struct file *file, unsigned int cmd, unsigned long arg)
 
 	if ((kinfo.mask & PIDFD_INFO_COREDUMP) && !(kinfo.coredump_mask)) {
 		task_lock(task);
-		if (task->mm)
-			kinfo.coredump_mask = pidfs_coredump_mask(task->mm->flags);
+		if (task->mm) {
+			unsigned long flags = __mm_flags_get_dumpable(task->mm);
+
+			kinfo.coredump_mask = pidfs_coredump_mask(flags);
+		}
 		task_unlock(task);
 	}
 
diff --git a/fs/proc/base.c b/fs/proc/base.c
index 62d35631ba8c..f0c093c58aaf 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2962,8 +2962,10 @@ static ssize_t proc_coredump_filter_read(struct file *file, char __user *buf,
 	ret = 0;
 	mm = get_task_mm(task);
 	if (mm) {
+		unsigned long flags = __mm_flags_get_dumpable(mm);
+
 		len = snprintf(buffer, sizeof(buffer), "%08lx\n",
-			       ((mm->flags & MMF_DUMP_FILTER_MASK) >>
+			       ((flags & MMF_DUMP_FILTER_MASK) >>
 				MMF_DUMP_FILTER_SHIFT));
 		mmput(mm);
 		ret = simple_read_from_buffer(buf, count, ppos, buffer, len);
@@ -3002,9 +3004,9 @@ static ssize_t proc_coredump_filter_write(struct file *file,
 
 	for (i = 0, mask = 1; i < MMF_DUMP_FILTER_BITS; i++, mask <<= 1) {
 		if (val & mask)
-			set_bit(i + MMF_DUMP_FILTER_SHIFT, &mm->flags);
+			mm_flags_set(i + MMF_DUMP_FILTER_SHIFT, mm);
 		else
-			clear_bit(i + MMF_DUMP_FILTER_SHIFT, &mm->flags);
+			mm_flags_clear(i + MMF_DUMP_FILTER_SHIFT, mm);
 	}
 
 	mmput(mm);
diff --git a/include/linux/sched/coredump.h b/include/linux/sched/coredump.h
index 6eb65ceed213..19ecfcceb27a 100644
--- a/include/linux/sched/coredump.h
+++ b/include/linux/sched/coredump.h
@@ -2,12 +2,29 @@
 #ifndef _LINUX_SCHED_COREDUMP_H
 #define _LINUX_SCHED_COREDUMP_H
 
+#include <linux/compiler_types.h>
 #include <linux/mm_types.h>
 
 #define SUID_DUMP_DISABLE	0	/* No setuid dumping */
 #define SUID_DUMP_USER		1	/* Dump as user of process */
 #define SUID_DUMP_ROOT		2	/* Dump as root */
 
+static inline unsigned long __mm_flags_get_dumpable(struct mm_struct *mm)
+{
+	/*
+	 * By convention, dumpable bits are contained in first 32 bits of the
+	 * bitmap, so we can simply access this first unsigned long directly.
+	 */
+	return __mm_flags_get_word(mm);
+}
+
+static inline void __mm_flags_set_mask_dumpable(struct mm_struct *mm, int value)
+{
+	unsigned long *bitmap = ACCESS_PRIVATE(&mm->_flags, __mm_flags);
+
+	set_mask_bits(bitmap, MMF_DUMPABLE_MASK, value);
+}
+
 extern void set_dumpable(struct mm_struct *mm, int value);
 /*
  * This returns the actual value of the suid_dumpable flag. For things
@@ -22,7 +39,9 @@ static inline int __get_dumpable(unsigned long mm_flags)
 
 static inline int get_dumpable(struct mm_struct *mm)
 {
-	return __get_dumpable(mm->flags);
+	unsigned long flags = __mm_flags_get_dumpable(mm);
+
+	return __get_dumpable(flags);
 }
 
 #endif /* _LINUX_SCHED_COREDUMP_H */
-- 
2.50.1