journal: fix access to munmapped memory in sd_journal_enumerate_unique

sd_j_e_u needs to keep a reference to an object while comparing it
with possibly duplicate objects in other files. Because the size of
mmap cache is limited, with enough files and object to compare to,
at some point the object being compared would be munmapped, resulting
in a segmentation fault.

Fix this issue by turning keep_always into a reference count that can
be increased and decreased. Other callers which set keep_always=true
are unmodified: their references are never released but are ignored
when the whole file is closed, which happens at some point. keep_always
is increased in sd_j_e_u and later on released.

1 files changed, 1 insertions, 4 deletions

diff --git a/src/journal/journal-file.c b/src/journal/journal-file.c
index 275324b67..b3747e37e 100644
--- a/src/journal/journal-file.c
+++ b/src/journal/journal-file.c
@@ -419,7 +419,6 @@ int journal_file_move_to_object(JournalFile *f, int type, uint64_t offset, Objec
         void *t;
         Object *o;
         uint64_t s;
-        unsigned context;
 
         assert(f);
         assert(ret);
@@ -428,10 +427,8 @@ int journal_file_move_to_object(JournalFile *f, int type, uint64_t offset, Objec
         if (!VALID64(offset))
                 return -EFAULT;
 
-        /* One context for each type, plus one catch-all for the rest */
-        context = type > 0 && type < _OBJECT_TYPE_MAX ? type : 0;
 
-        r = journal_file_move_to(f, context, false, offset, sizeof(ObjectHeader), &t);
+        r = journal_file_move_to(f, type_to_context(type), false, offset, sizeof(ObjectHeader), &t);
         if (r < 0)
                 return r;