pstore/ram: fix resource leak when ioremap() fails

In persistent_ram_iomap(), ioremap() or ioremap_wc() may return NULL on
failure. Currently, if this happens, the function returns NULL without
releasing the memory region acquired by request_mem_region().

This leads to a resource leak where the memory region remains reserved
but unusable.

Additionally, the caller persistent_ram_buffer_map() handles NULL
correctly by returning -ENOMEM, but without this check, a NULL return
combined with request_mem_region() succeeding leaves resources in an
inconsistent state.

This is the ioremap() counterpart to commit 05363ab ("pstore:
ram_core: fix incorrect success return when vmap() fails") which fixed
a similar issue in the vmap() path.

Fixes: 404a604 ("staging: android: persistent_ram: handle reserving and mapping memory")
Signed-off-by: Cole Leavitt <cole@unwrap.rs>
Link: https://patch.msgid.link/20260225235406.11790-1-cole@unwrap.rs
Signed-off-by: Kees Cook <kees@kernel.org>

Author: coleleavitt

fs/pstore/ram_core.c

@@ -487,6 +487,10 @@ static void *persistent_ram_iomap(phys_addr_t start, size_t size,
 	else
 		va = ioremap_wc(start, size);
 
+	/* We must release the mem region if ioremap fails. */
+	if (!va)
+		release_mem_region(start, size);
+
 	/*
 	 * Since request_mem_region() and ioremap() are byte-granularity
 	 * there is no need handle anything special like we do when the