From 11dd5b2a511fc0617bc06a3db99a7ea51ea209bd Mon Sep 17 00:00:00 2001
From: Tulio A M Mendes <tadryanom@hotmail.com>
Date: Tue, 26 May 2026 02:09:59 -0300
Subject: [PATCH] security: add complete POSIX permissions for SHM (Fase 2)

---
 include/shm.h    |  6 ++++++
 src/kernel/shm.c | 56 ++++++++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 60 insertions(+), 2 deletions(-)

diff --git a/include/shm.h b/include/shm.h
index 971c136d..09facf4b 100644
--- a/include/shm.h
+++ b/include/shm.h
@@ -23,14 +23,20 @@
 /* Commands for shmctl */
 #define IPC_RMID    0
 #define IPC_STAT    1
+#define IPC_SET     2
 
 /* Private key — always creates a new segment */
 #define IPC_PRIVATE 0
 
+struct ipc_perm {
+    uint32_t mode;          /* permission mode */
+};
+
 struct shmid_ds {
     uint32_t shm_segsz;     /* segment size in bytes */
     uint32_t shm_nattch;    /* number of current attaches */
     uint32_t shm_key;       /* key */
+    struct ipc_perm shm_perm; /* permission structure */
 };
 
 /* Kernel API */
diff --git a/src/kernel/shm.c b/src/kernel/shm.c
index 42ccda5a..67124c41 100644
--- a/src/kernel/shm.c
+++ b/src/kernel/shm.c
@@ -55,6 +55,29 @@ static void shm_destroy(struct shm_segment* seg) {
     memset(seg, 0, sizeof(*seg));
 }
 
+/* Check POSIX permission for SHM segment */
+static int shm_perm_check(struct shm_segment* seg, int perm) {
+    if (!current_process) return 0;
+    if (current_process->euid == 0) return 1;  /* Root can do anything */
+
+    uint32_t mode = seg->mode;
+    uint32_t uid = seg->uid;
+    uint32_t gid = seg->gid;
+
+    /* Owner permissions */
+    if (current_process->uid == uid || current_process->euid == uid) {
+        return (mode & (perm << 6)) != 0;
+    }
+
+    /* Group permissions */
+    if (current_process->gid == gid || current_process->egid == gid) {
+        return (mode & (perm << 3)) != 0;
+    }
+
+    /* Other permissions */
+    return (mode & perm) != 0;
+}
+
 int shm_get(uint32_t key, uint32_t size, int flags) {
     if (size == 0) return -EINVAL;
 
@@ -143,8 +166,8 @@ void* shm_at(int shmid, uintptr_t shmaddr) {
         return (void*)(uintptr_t)-EINVAL;
     }
 
-    /* K14: Check permission - owner or root only */
-    if (seg->uid != current_process->uid && current_process->uid != 0) {
+    /* Check POSIX read permission */
+    if (!shm_perm_check(seg, 04)) {  /* R_OK = 4 */
         spin_unlock_irqrestore(&shm_lock, irqf);
         return (void*)(uintptr_t)-EACCES;
     }
@@ -264,6 +287,11 @@ int shm_ctl(int shmid, int cmd, struct shmid_ds* buf) {
     }
 
     if (cmd == IPC_STAT) {
+        /* Check read permission */
+        if (!shm_perm_check(seg, 04)) {
+            spin_unlock_irqrestore(&shm_lock, irqf);
+            return -EACCES;
+        }
         /* Copy to local struct first, then release lock before
          * writing to userspace to avoid deadlock on page fault. */
         struct shmid_ds local;
@@ -280,6 +308,11 @@ int shm_ctl(int shmid, int cmd, struct shmid_ds* buf) {
     }
 
     if (cmd == IPC_RMID) {
+        /* Only owner or root can remove */
+        if (seg->uid != current_process->uid && current_process->euid != 0) {
+            spin_unlock_irqrestore(&shm_lock, irqf);
+            return -EPERM;
+        }
         if (seg->nattch == 0) {
             shm_destroy(seg);
         } else {
@@ -289,6 +322,25 @@ int shm_ctl(int shmid, int cmd, struct shmid_ds* buf) {
         return 0;
     }
 
+    if (cmd == IPC_SET) {
+        /* Only owner or root can change permissions */
+        if (seg->uid != current_process->uid && current_process->euid != 0) {
+            spin_unlock_irqrestore(&shm_lock, irqf);
+            return -EPERM;
+        }
+        if (buf) {
+            struct shmid_ds local;
+            if (copy_from_user(&local, buf, sizeof(local)) < 0) {
+                spin_unlock_irqrestore(&shm_lock, irqf);
+                return -EFAULT;
+            }
+            /* Update mode from IPC_SET */
+            seg->mode = local.shm_perm.mode & 0777;
+        }
+        spin_unlock_irqrestore(&shm_lock, irqf);
+        return 0;
+    }
+
     spin_unlock_irqrestore(&shm_lock, irqf);
     return -EINVAL;
 }
-- 
2.43.0