[PATCH] ACPI: OSL: Fix a NULL pointer dereference in extlog_init().

[Zhou Qingyang <zhou1615@umn.edu>]

In extlog_init(), acpi_os_map_iomem() is assigned to extlog_l1_hdr and
there is a dereference of it through l1_head. on the failure of
acpi_os_map_iomem(), the return value of it could be NULL, which may
introduce a NULL pointer dereference.

Fix this bug by adding a NULL check of extlog_l1_hdr.

This bug was found by a static analyzer.

Builds with 'make allyesconfig' show no new warnings,
and our static analyzer no longer warns about this code.

Fixes: a238317ce818 ("ACPI: Clean up acpi_os_map/unmap_memory() to eliminate __iomem.")
Signed-off-by: Zhou Qingyang <zhou1615@umn.edu>
---
The analysis employs differential checking to identify inconsistent 
security operations (e.g., checks or kfrees) between two code paths 
and confirms that the inconsistent operations are not recovered in the
current function or the callers, so they constitute bugs. 

Note that, as a bug found by static analysis, it can be a false
positive or hard to trigger. Multiple researchers have cross-reviewed
the bug.

 drivers/acpi/acpi_extlog.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/acpi/acpi_extlog.c b/drivers/acpi/acpi_extlog.c
index 72f1fb77abcd..2187ac23d3d4 100644
--- a/drivers/acpi/acpi_extlog.c
+++ b/drivers/acpi/acpi_extlog.c
@@ -239,6 +239,12 @@ static int __init extlog_init(void)
 	}
 
 	extlog_l1_hdr = acpi_os_map_iomem(l1_dirbase, l1_hdr_size);
+	if (!extlog_l1_hdr) {
+		rc = -ENOMEM;
+		release_mem_region(l1_dirbase, l1_hdr_size);
+		goto err;
+	}
+
 	l1_head = (struct extlog_l1_head *)extlog_l1_hdr;
 	l1_size = l1_head->total_len;
 	l1_percpu_entry = l1_head->entries;
-- 
2.25.1