The patch titled
Subject: mm: refactor mm_access() to not return NULL
has been added to the -mm mm-unstable branch. Its filename is
mm-refactor-mm_access-to-not-return-null.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-refactor-mm_access-to-not-return-null.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
Subject: mm: refactor mm_access() to not return NULL
Date: Tue, 24 Sep 2024 21:10:23 +0100
mm_access() can return NULL if the mm is not found, but this is handled
the same as an error in all callers, with some translating this into an
-ESRCH error.
Only proc_mem_open() returns NULL if no mm is found, however in this case
it is clearer and makes more sense to explicitly handle the error.
Additionally we take the opportunity to refactor the function to eliminate
unnecessary nesting.
Simplify things by simply returning -ESRCH if no mm is found - this both
eliminates confusing use of the IS_ERR_OR_NULL() macro, and simplifies
callers which would return -ESRCH by returning this error directly.
Link: https://lkml.kernel.org/r/20240924201023.193135-1-lorenzo.stoakes@xxxxxxxxxx
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
Suggested-by: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/proc/base.c | 26 ++++++++++++++------------
kernel/fork.c | 5 +++--
mm/madvise.c | 4 ++--
mm/process_vm_access.c | 4 ++--
4 files changed, 21 insertions(+), 18 deletions(-)
--- a/fs/proc/base.c~mm-refactor-mm_access-to-not-return-null
+++ a/fs/proc/base.c
@@ -832,19 +832,21 @@ static const struct file_operations proc
struct mm_struct *proc_mem_open(struct inode *inode, unsigned int mode)
{
struct task_struct *task = get_proc_task(inode);
- struct mm_struct *mm = ERR_PTR(-ESRCH);
+ struct mm_struct *mm;
- if (task) {
- mm = mm_access(task, mode | PTRACE_MODE_FSCREDS);
- put_task_struct(task);
+ if (!task)
+ return ERR_PTR(-ESRCH);
- if (!IS_ERR_OR_NULL(mm)) {
- /* ensure this mm_struct can't be freed */
- mmgrab(mm);
- /* but do not pin its memory */
- mmput(mm);
- }
- }
+ mm = mm_access(task, mode | PTRACE_MODE_FSCREDS);
+ put_task_struct(task);
+
+ if (IS_ERR(mm))
+ return PTR_ERR(mm) == -ESRCH ? NULL : mm;
+
+ /* ensure this mm_struct can't be freed */
+ mmgrab(mm);
+ /* but do not pin its memory */
+ mmput(mm);
return mm;
}
@@ -2208,7 +2210,7 @@ static int map_files_d_revalidate(struct
goto out_notask;
mm = mm_access(task, PTRACE_MODE_READ_FSCREDS);
- if (IS_ERR_OR_NULL(mm))
+ if (IS_ERR(mm))
goto out;
if (!dname_to_vma_addr(dentry, &vm_start, &vm_end)) {
--- a/kernel/fork.c~mm-refactor-mm_access-to-not-return-null
+++ a/kernel/fork.c
@@ -1545,8 +1545,9 @@ struct mm_struct *mm_access(struct task_
return ERR_PTR(err);
mm = get_task_mm(task);
- if (mm && mm != current->mm &&
- !ptrace_may_access(task, mode)) {
+ if (!mm) {
+ mm = ERR_PTR(-ESRCH);
+ } else if (mm != current->mm && !ptrace_may_access(task, mode)) {
mmput(mm);
mm = ERR_PTR(-EACCES);
}
--- a/mm/madvise.c~mm-refactor-mm_access-to-not-return-null
+++ a/mm/madvise.c
@@ -1537,8 +1537,8 @@ SYSCALL_DEFINE5(process_madvise, int, pi
/* Require PTRACE_MODE_READ to avoid leaking ASLR metadata. */
mm = mm_access(task, PTRACE_MODE_READ_FSCREDS);
- if (IS_ERR_OR_NULL(mm)) {
- ret = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH;
+ if (IS_ERR(mm)) {
+ ret = PTR_ERR(mm);
goto release_task;
}
--- a/mm/process_vm_access.c~mm-refactor-mm_access-to-not-return-null
+++ a/mm/process_vm_access.c
@@ -201,8 +201,8 @@ static ssize_t process_vm_rw_core(pid_t
}
mm = mm_access(task, PTRACE_MODE_ATTACH_REALCREDS);
- if (!mm || IS_ERR(mm)) {
- rc = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH;
+ if (IS_ERR(mm)) {
+ rc = PTR_ERR(mm);
/*
* Explicitly map EACCES to EPERM as EPERM is a more
* appropriate error code for process_vw_readv/writev
_
Patches currently in -mm which might be from lorenzo.stoakes@xxxxxxxxxx are
tools-fix-shared-radix-tree-build.patch
selftests-mm-add-pkey_sighandler_xx-hugetlb_dio-to-gitignore.patch
mm-madvise-introduce-pr_madv_self-flag-to-process_madvise.patch
selftests-mm-add-test-for-process_madvise-pr_madv_self-flag-use.patch
mm-refactor-mm_access-to-not-return-null.patch
mm-refactor-mm_access-to-not-return-null-fix.patch
