JFFS2: Add parameter to reserve disk space for root

Add a new rp_size= parameter which creates a "reserved pool" of disk
space which can only be used by root. Other users are not permitted
to write to disk when the available space is less than the pool size.

Based on original code by Artem Bityutskiy in
https://dev.laptop.org/ticket/5317

[dwmw2: use capable(CAP_SYS_RESOURCE) not uid/gid check, fix debug prints]
Signed-off-by: Daniel Drake <dsd@laptop.org>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

1 files changed, 42 insertions, 0 deletions

diff --git a/fs/jffs2/nodemgmt.c b/fs/jffs2/nodemgmt.c
index 6784d1e..0c96eb5 100644
--- a/fs/jffs2/nodemgmt.c
+++ b/fs/jffs2/nodemgmt.c
@@ -18,6 +18,37 @@
 #include "nodelist.h"
 #include "debug.h"
 
+/*
+ * Check whether the user is allowed to write.
+ */
+static int jffs2_rp_can_write(struct jffs2_sb_info *c)
+{
+	uint32_t avail;
+	struct jffs2_mount_opts *opts = &c->mount_opts;
+
+	avail = c->dirty_size + c->free_size + c->unchecked_size +
+		c->erasing_size - c->resv_blocks_write * c->sector_size
+		- c->nospc_dirty_size;
+
+	if (avail < 2 * opts->rp_size)
+		jffs2_dbg(1, "rpsize %u, dirty_size %u, free_size %u, "
+			  "erasing_size %u, unchecked_size %u, "
+			  "nr_erasing_blocks %u, avail %u, resrv %u\n",
+			  opts->rp_size, c->dirty_size, c->free_size,
+			  c->erasing_size, c->unchecked_size,
+			  c->nr_erasing_blocks, avail, c->nospc_dirty_size);
+
+	if (avail > opts->rp_size)
+		return 1;
+
+	/* Always allow root */
+	if (capable(CAP_SYS_RESOURCE))
+		return 1;
+
+	jffs2_dbg(1, "forbid writing\n");
+	return 0;
+}
+
 /**
  *	jffs2_reserve_space - request physical space to write nodes to flash
  *	@c: superblock info
@@ -55,6 +86,15 @@ int jffs2_reserve_space(struct jffs2_sb_info *c, uint32_t minsize,
 
 	spin_lock(&c->erase_completion_lock);
 
+	/*
+	 * Check if the free space is greater then size of the reserved pool.
+	 * If not, only allow root to proceed with writing.
+	 */
+	if (prio != ALLOC_DELETION && !jffs2_rp_can_write(c)) {
+		ret = -ENOSPC;
+		goto out;
+	}
+
 	/* this needs a little more thought (true <tglx> :)) */
 	while(ret == -EAGAIN) {
 		while(c->nr_free_blocks + c->nr_erasing_blocks < blocksneeded) {
@@ -158,6 +198,8 @@ int jffs2_reserve_space(struct jffs2_sb_info *c, uint32_t minsize,
 			jffs2_dbg(1, "%s(): ret is %d\n", __func__, ret);
 		}
 	}
+
+out:
 	spin_unlock(&c->erase_completion_lock);
 	if (!ret)
 		ret = jffs2_prealloc_raw_node_refs(c, c->nextblock, 1);