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Subject[PATCH v3 3/5] sysctl: fold sysctl_writes_strict checks into helper
Date
The mode sysctl_writes_strict positional checks keep being
copy and pasted as we add new proc handlers. Just add a helper
to avoid code duplication.

Suggested-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>
---
kernel/sysctl.c | 56 ++++++++++++++++++++++++++++++++------------------------
1 file changed, 32 insertions(+), 24 deletions(-)

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 02725178694a..6f3bb1f099fa 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1971,6 +1971,32 @@ static void warn_sysctl_write(struct ctl_table *table)
}

/**
+ * proc_first_pos_non_zero_ignore - check if firs position is allowed
+ * @ppos: file position
+ * @table: the sysctl table
+ *
+ * Returns true if the first position is non-zero and the sysctl_writes_strict
+ * mode indicates this is not allowed for numeric input types. String proc
+ * hadlers can ignore the return value.
+ */
+static bool proc_first_pos_non_zero_ignore(loff_t *ppos,
+ struct ctl_table *table)
+{
+ if (!*ppos)
+ return false;
+
+ switch (sysctl_writes_strict) {
+ case SYSCTL_WRITES_STRICT:
+ return true;
+ case SYSCTL_WRITES_WARN:
+ warn_sysctl_write(table);
+ return false;
+ default:
+ return false;
+ }
+}
+
+/**
* proc_dostring - read a string sysctl
* @table: the sysctl table
* @write: %TRUE if this is a write to the sysctl file
@@ -1990,8 +2016,8 @@ static void warn_sysctl_write(struct ctl_table *table)
int proc_dostring(struct ctl_table *table, int write,
void __user *buffer, size_t *lenp, loff_t *ppos)
{
- if (write && *ppos && sysctl_writes_strict == SYSCTL_WRITES_WARN)
- warn_sysctl_write(table);
+ if (write)
+ proc_first_pos_non_zero_ignore(ppos, table);

return _proc_do_string((char *)(table->data), table->maxlen, write,
(char __user *)buffer, lenp, ppos);
@@ -2193,17 +2219,8 @@ static int __do_proc_dointvec(void *tbl_data, struct ctl_table *table,
conv = do_proc_dointvec_conv;

if (write) {
- if (*ppos) {
- switch (sysctl_writes_strict) {
- case SYSCTL_WRITES_STRICT:
- goto out;
- case SYSCTL_WRITES_WARN:
- warn_sysctl_write(table);
- break;
- default:
- break;
- }
- }
+ if (proc_first_pos_non_zero_ignore(ppos, table))
+ goto out;

if (left > PAGE_SIZE - 1)
left = PAGE_SIZE - 1;
@@ -2468,17 +2485,8 @@ static int __do_proc_doulongvec_minmax(void *data, struct ctl_table *table, int
left = *lenp;

if (write) {
- if (*ppos) {
- switch (sysctl_writes_strict) {
- case SYSCTL_WRITES_STRICT:
- goto out;
- case SYSCTL_WRITES_WARN:
- warn_sysctl_write(table);
- break;
- default:
- break;
- }
- }
+ if (proc_first_pos_non_zero_ignore(ppos, table))
+ goto out;

if (left > PAGE_SIZE - 1)
left = PAGE_SIZE - 1;
--
2.11.0
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