[PATCH 2/3] fs/proc/task_mmu.c: check the return value of mpol_to_str()

[Chen Gang]

mpol_to_str() may fail, and not fill the buffer (e.g. -EINVAL), so need
check about it, or buffer may not be zero based, and next seq_printf()
will cause issue.

Also print related warning when the buffer space is not enough.


Signed-off-by: Chen Gang <gang.chen@xxxxxxxxxxx>
---
 fs/proc/task_mmu.c |   16 ++++++++++++++--
 1 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index a117207..1cb7445 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -1359,7 +1359,7 @@ static int show_numa_map(struct seq_file *m, void *v, int is_pid)
 	struct mm_struct *mm = vma->vm_mm;
 	struct mm_walk walk = {};
 	struct mempolicy *pol;
-	int n;
+	int n, ret;
 	char buffer[50];
 
 	if (!mm)
@@ -1376,7 +1376,19 @@ static int show_numa_map(struct seq_file *m, void *v, int is_pid)
 	walk.mm = mm;
 
 	pol = get_vma_policy(task, vma, vma->vm_start);
-	mpol_to_str(buffer, sizeof(buffer), pol);
+	ret = mpol_to_str(buffer, sizeof(buffer), pol);
+	if (ret < 0)
+		switch (ret) {
+		case -ENOSPC:
+			pr_warn("in %s: string is truncated in mpol_to_str().\n",
+				__func__);
+			break;
+		default:
+			pr_err("in %s: call mpol_to_str() fail, errcode: %d. buffer: %p, size: %zu,  pol: %p\n",
+				__func__, ret, buffer, sizeof(buffer), pol);
+			return ret;
+		}
+
 	mpol_cond_put(pol);
 
 	seq_printf(m, "%08lx %s", vma->vm_start, buffer);
-- 
1.7.7.6
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