[PATCH] bcachefs: Fix refs to undefined fields in __bch2_alloc_v4_to_text()

[Kent Overstreet]

Recent stack usage reductions have avoided unpacking alloc keys onto the
stack in a few places, but when we do so we must be careful not to
reference fields that don't exist - key values can be extended with new
fields over time.

Reported-by: syzbot+8eb51728519f6659e...@syzkaller.appspotmail.com
Fixes: eabef52ff881 ("bcachefs: bch2_alloc_v4_to_text()")
Signed-off-by: Kent Overstreet <kent.overstr...@linux.dev>
---
 fs/bcachefs/alloc_background.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/fs/bcachefs/alloc_background.c b/fs/bcachefs/alloc_background.c
index 4c1604fd80f9..f1d35b7f3fc5 100644
--- a/fs/bcachefs/alloc_background.c
+++ b/fs/bcachefs/alloc_background.c
@@ -337,9 +337,10 @@ void bch2_alloc_v4_swab(struct bkey_s k)
 }
 
 static inline void __bch2_alloc_v4_to_text(struct printbuf *out, struct bch_fs 
*c,
-                                          unsigned dev, const struct 
bch_alloc_v4 *a)
+                                          struct bkey_s_c k,
+                                          const struct bch_alloc_v4 *a)
 {
-       struct bch_dev *ca = c ? bch2_dev_tryget_noerror(c, dev) : NULL;
+       struct bch_dev *ca = c ? bch2_dev_tryget_noerror(c, k.k->p.inode) : 
NULL;
 
        prt_newline(out);
        printbuf_indent_add(out, 2);
@@ -348,11 +349,14 @@ static inline void __bch2_alloc_v4_to_text(struct 
printbuf *out, struct bch_fs *
        bch2_prt_data_type(out, a->data_type);
        prt_newline(out);
        prt_printf(out, "journal_seq_nonempty %llu\n",  
a->journal_seq_nonempty);
-       prt_printf(out, "journal_seq_empty    %llu\n",  a->journal_seq_empty);
+       if (bkey_val_bytes(k.k) > offsetof(struct bch_alloc_v4, 
journal_seq_empty))
+               prt_printf(out, "journal_seq_empty    %llu\n",  
a->journal_seq_empty);
+
        prt_printf(out, "need_discard         %llu\n",  
BCH_ALLOC_V4_NEED_DISCARD(a));
        prt_printf(out, "need_inc_gen         %llu\n",  
BCH_ALLOC_V4_NEED_INC_GEN(a));
        prt_printf(out, "dirty_sectors        %u\n",    a->dirty_sectors);
-       prt_printf(out, "stripe_sectors       %u\n",    a->stripe_sectors);
+       if (bkey_val_bytes(k.k) > offsetof(struct bch_alloc_v4, stripe_sectors))
+               prt_printf(out, "stripe_sectors       %u\n",    
a->stripe_sectors);
        prt_printf(out, "cached_sectors       %u\n",    a->cached_sectors);
        prt_printf(out, "stripe               %u\n",    a->stripe);
        prt_printf(out, "stripe_redundancy    %u\n",    a->stripe_redundancy);
@@ -372,12 +376,12 @@ void bch2_alloc_to_text(struct printbuf *out, struct 
bch_fs *c, struct bkey_s_c
        struct bch_alloc_v4 _a;
        const struct bch_alloc_v4 *a = bch2_alloc_to_v4(k, &_a);
 
-       __bch2_alloc_v4_to_text(out, c, k.k->p.inode, a);
+       __bch2_alloc_v4_to_text(out, c, k, a);
 }
 
 void bch2_alloc_v4_to_text(struct printbuf *out, struct bch_fs *c, struct 
bkey_s_c k)
 {
-       __bch2_alloc_v4_to_text(out, c, k.k->p.inode, 
bkey_s_c_to_alloc_v4(k).v);
+       __bch2_alloc_v4_to_text(out, c, k, bkey_s_c_to_alloc_v4(k).v);
 }
 
 void __bch2_alloc_to_v4(struct bkey_s_c k, struct bch_alloc_v4 *out)
-- 
2.50.0